examples/ipsec-secgw: fix inbound crash
examples/ipsec-secgw: fix inbound crash

When sending Inbound non IPSec traffic that matches an Inbound Security
Policy set to Protect, the code will check that the SPI of the packet
and the associated Security Association match.

That check should only be done for IPSec packets and results in SEGFAULT
when done on non IPSec packets.

Fixes: 906257e965b7 ("examples/ipsec-secgw: support IPv6")

Signed-off-by: Sergio Gonzalez Monroy <efb28dd1236fe58fb57f933212eddfe89b9da704@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk