examples/ipsec-secgw: fix debug logs

examples/ipsec-secgw: fix debug logs

Improve debug code in esp.c, sa.c and ipsec-secgw.c

Fixes: f159e70b0922 ("examples/ipsec-secgw: support transport mode")
Fixes: ec17993a145a ("examples/ipsec-secgw: support security offload")
Fixes: 0d547ed03717 ("examples/ipsec-secgw: support configuration file")
Fixes: 906257e965b7 ("examples/ipsec-secgw: support IPv6")
Cc: stable@dpdk.org
Signed-off-by: Bernard Iremonger <bernard.iremonger@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>