classify: fix crash when update nonexistent classify table.
classify: fix crash when update nonexistent classify table.

vpp crash when update nonexistent classify table.
Program received signal SIGABRT, Aborted.
0x00007fbf3b49b337 in raise () from /lib64/libc.so.6
(gdb) bt
0  0x00007fbf3b49b337 in raise () from /lib64/libc.so.6
1  0x00007fbf3b49ca28 in abort () from /lib64/libc.so.6
2  0x00000000004079db in os_panic () at /usr/src/debug/vpp-23.02/src/vpp/vnet/main.c:417
3  0x00007fbf3bb611c7 in debugger () at /usr/src/debug/vpp-23.02/src/vppinfra/error.c:84
4  0x00007fbf3bb61529 in _clib_error (how_to_die=2, function_name=0x0, line_number=0, fmt=0x7fbf3d03af08 "%s:%d (%s) assertion `%s' fails")
   at /usr/src/debug/vpp-23.02/src/vppinfra/error.c:143
5  0x00007fbf3c67062c in vnet_classify_add_del_table (cm=0x7fbf3d438f00 <vnet_classify_main>, mask=0x7fbf00fdc088 "", nbuckets=2, memory_size=2097152,
   skip=4, match=1, next_table_index=4294967295, miss_next_index=4294967295, table_index=0x7fbeed930b98, current_data_flag=0 '\000',
   current_data_offset=0, is_add=1, del_chain=0) at /usr/src/debug/vpp-23.02/src/vnet/classify/vnet_classify.c:780
6  0x00007fbf3c672bf4 in classify_table_command_fn (vm=0x7fbefb465740, input=0x7fbeed930ef0, cmd=0x7fbefc45ec18)
   at /usr/src/debug/vpp-23.02/src/vnet/classify/vnet_classify.c:1622
7  0x00007fbf3d52b527 in vlib_cli_dispatch_sub_commands (vm=0x7fbefb465740, cm=0x4273f0 <vlib_global_main+48>, input=0x7fbeed930ef0,
   parent_command_index=1064) at /usr/src/debug/vpp-23.02/src/vlib/cli.c:650
8  0x00007fbf3d52b2c3 in vlib_cli_dispatch_sub_commands (vm=0x7fbefb465740, cm=0x4273f0 <vlib_global_main+48>, input=0x7fbeed930ef0,
   parent_command_index=0) at /usr/src/debug/vpp-23.02/src/vlib/cli.c:607
9  0x00007fbf3d52b9cb in vlib_cli_input (vm=0x7fbefb465740, input=0x7fbeed930ef0, function=0x7fbf3d597406 <unix_vlib_cli_output>, function_arg=0)
   at /usr/src/debug/vpp-23.02/src/vlib/cli.c:753
10 0x00007fbf3d59cb0c in unix_cli_process_input (cm=0x7fbf3d61fe00 <unix_cli_main>, cli_file_index=0)
   at /usr/src/debug/vpp-23.02/src/vlib/unix/cli.c:2616
11 0x00007fbf3d59d25a in unix_cli_process (vm=0x7fbefb465740, rt=0x7fbf00f7bfc0, f=0x0) at /usr/src/debug/vpp-23.02/src/vlib/unix/cli.c:2745
12 0x00007fbf3d555a25 in vlib_process_bootstrap (_a=140458063833296) at /usr/src/debug/vpp-23.02/src/vlib/main.c:1221
13 0x00007fbf3bb74204 in clib_calljmp () at /usr/src/debug/vpp-23.02/src/vppinfra/longjmp.S:123
14 0x00007fbef10028a0 in ?? ()
15 0x00007fbf3d555b4e in vlib_process_startup (vm=0x7fbf3bb7d70f <clib_mem_size+24>, p=0x7fbef10028d0, f=0x7fbf00f06ae0)
   at /usr/src/debug/vpp-23.02/src/vlib/main.c:1246
16 0x00007fbf3d592be6 in vec_max_bytes (v=0x8) at /usr/src/debug/vpp-23.02/src/vppinfra/vec_bootstrap.h:161
17 0x00007fbf00f06af8 in ?? ()
18 0x0000000000000004 in ?? ()
19 0x00000000000000ff in ?? ()
20 0x00007fbef1002980 in ?? ()
21 0x00007fbf3d592dcb in _vec_set_len (v=<error reading variable: Cannot access memory at address 0xfffffffffffffff5>,
   len=<error reading variable: Cannot access memory at address 0xffffffffffffffed>,
   elt_sz=<error reading variable: Cannot access memory at address 0xffffffffffffffe5>) at /usr/src/debug/vpp-23.02/src/vppinfra/vec_bootstrap.h:196
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
(gdb) f 5
   0x00007fbf3c67062c in vnet_classify_add_del_table (cm=0x7fbf3d438f00 <vnet_classify_main>, mask=0x7fbf00fdc088 "", nbuckets=2, memory_size=2097152,
   skip=4, match=1, next_table_index=4294967295, miss_next_index=4294967295, table_index=0x7fbeed930b98, current_data_flag=0 '\000',
   current_data_offset=0, is_add=1, del_chain=0) at /usr/src/debug/vpp-23.02/src/vnet/classify/vnet_classify.c:780
780		  t = pool_elt_at_index (cm->tables, *table_index);
(gdb) p *table_index
$1 = 8
(gdb) p cm->tables
$2 = (vnet_classify_table_t *) 0x0
(gdb)

Type: fix

Signed-off-by: Huawei LI <59bd70945e7d500d33dc12e5139b7e4ae4ab4f96@163.com>
Change-Id: I1c5f6168f0a7e1d1989ce07ec6c30c6fd9f0aaa9

FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp