tapv2: coverity strikes back

tapv2: coverity strikes back

while https://gerrit.fd.io/r/#/c/16590/ fixed the leaked fd which coverity
reported at that time, new coverity run reports simailar leaked fd in a
different goto punt path. It would be nice if coverity reported both of them
at the same time. Or perhaps it did and I just missed it. Anyway, the new fix
is to put the close (fd) statement prior to the return of tap_create_if routine
which should catch all goto's.

Change-Id: I0a51ed3710e32d5d74c9cd9b5066a667153e2f9d
Signed-off-by: Steven Luong <sluong@cisco.com>