examples/ipsec-secgw: fix build on FreeBSD

examples/ipsec-secgw: fix build on FreeBSD

In FreeBSD, sys/types.h and netinet/in.h need to be included before
netinet/ip.h

There were missed typedef for u_char - <sys/types.h>
There were missed network definitions - <netinet/in.h>

Failure #13: http://dpdk.org/ml/archives/test-report/2016-March/001896.html

Fixes: d299106e8e31 ("examples/ipsec-secgw: add IPsec sample application")
Signed-off-by: Daniel Mrzyglod <danielx.t.mrzyglod@intel.com>
Acked-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>