tap: Fix tap create with ns

This fixes the interface creation passing
a netns. [0] made the renaming of the new
tuntap interface before switching netns
Thus, preventing creating an interface in
another netns if one exists in VPP's netns
with the same name.
This also fixes restore netns on errors

Type: fix

[0] https://gerrit.fd.io/r/c/vpp/+/33696

Change-Id: I5c83bb37d664057bcf231cd0c636f0e51aa542ad
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>