examples/ipsec-secgw: fix configuration string termination
examples/ipsec-secgw: fix configuration string termination

Coverity issue: 137854, 137855
Fixes: 0d547ed03717 ("examples/ipsec-secgw: support configuration file")

Signed-off-by: Fan Zhang <b46d470dc79aa6fd718cd24d07380f6203b7fc3c@intel.com>
Acked-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

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