mbuf.gdb: Print om_data as hexdump, not int array
mbuf.gdb: Print om_data as hexdump, not int array

E.g.,

BEFORE:
    Mbuf data: $528 = {0x68, 0x5d, 0x0, 0x20, 0x0, 0x8, 0x7c, 0x0, 0xb0,
    0x68, 0x0, 0x20, 0x38, 0x5c, 0x0, 0x20, 0xff, 0x0, 0x0, 0x0, 0xe8, 0x59,
    0x0, 0x20, 0x0, 0xff, 0x4, 0x19, 0x72, 0x46, 0xdf, 0x9, 0x21, 0xe7,
    [...]

AFTER:
    Mbuf data:
    0x200055b0 <os_msys_1_data+608>:        0x68    0x5d    0x00    0x20    0x00    0x08    0x7c    0x00
    0x200055b8 <os_msys_1_data+616>:        0xb0    0x68    0x00    0x20    0x38    0x5c    0x00    0x20
    [...]

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core