examples/ipsec-gw: fix build with pkg-config

examples/ipsec-gw: fix build with pkg-config

flow.c: In function ‘parse_flow_tokens’:
flow.c:153:23: error: taking address of packed member of ‘struct
rte_ipv4_hdr’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  153 |     if (ipv4_addr_cpy(&rule->ipv4.spec.hdr.src_addr,
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
flow.c:154:9: error: taking address of packed member of ‘struct
rte_ipv4_hdr’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  154 |         &rule->ipv4.mask.hdr.src_addr,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
flow.c:170:23: error: taking address of packed member of ‘struct
rte_ipv4_hdr’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  170 |     if (ipv4_addr_cpy(&rule->ipv4.spec.hdr.dst_addr,
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
flow.c:171:9: error: taking address of packed member of ‘struct
rte_ipv4_hdr’ may result in an unaligned pointer value
[-Werror=address-of-packed-member]
  171 |         &rule->ipv4.mask.hdr.dst_addr,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

Meson build is fine since we waive those warnings.
Replicate it for make.

Fixes: 8e693616fcb2 ("examples/ipsec-secgw: enable flow based distribution")
Cc: stable@dpdk.org
Signed-off-by: David Marchand <david.marchand@redhat.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>