tap: fix coverity warning 205875
tap: fix coverity warning 205875

check the return result from fcntl, and if error, behave
the same way the expansion of _IOCTL macro does.

Type: fix
Change-Id: I6d537d1bdedae64470612aef64b46e07387fe84b
Signed-off-by: Andrew Yourtchenko <eb6233fe2fbd585844f4fb8426b53b186ab379b1@gmail.com>

chrisy/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,vpp-dev/vpp