tap: fix the api for use of vec_len
tap: fix the api for use of vec_len

Type: fix

Fixes: 03b76a20c569b8275beb8783691300a7d66b54a4

Change-Id: Ife788974cb7b2c35f40a017dd195dc2f7ee797b4
Signed-off-by: Mohsin Kazmi <3be96aed1fe21f963e790909e1d3a8e57ce776f2@cisco.com>

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