misc: vppctl - fix coverity warning
misc: vppctl - fix coverity warning

Check that provided path fits into defined buffer. Don't write too many
bytes to avoid having an unterminated string.

Type: fix
Fixes: 31f192434660
Signed-off-by: Klement Sekera <b8003f27414ca85c37624503b7b4e8f8c829bb4d@cisco.com>
Change-Id: I1ea8b6d6a3474c032e542b6980ed14bac72093a8

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