linux-cp: fix coverity defect
linux-cp: fix coverity defect

Type: fix

If no host interface name is passed to the CLI command which creates
an interface pair, NULL gets passed to lcp_itf_pair_create() and a
seg fault occurs. Check whether a host interface name was provided
and fail gracefully if none was given.

Change-Id: I82886f4c2ee710e206c751c34a74399112e9062c
Signed-off-by: Matthew Smith <52a1745bd9fd6c0a26d8c7252aafb349bbdbd656@netgate.com>

chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp