tap: clean-up when linux will delete the tap interface

tap: clean-up when linux will delete the tap interface

When container is deleted which has tap interface attached,
Linux also delete the tap interface leaving the VPP side of
tap. This patch does a clean up job to remove that VPP side
of tap interface.

To produce the behavior:
In VPP:
  create tap
On linux:
  sudo ip netns add ns1
  sudo ip link set dev tap0 netns ns1
  sudo ip netns del ns1

Change-Id: Iaed1700073a9dc64e626c1d0c449f466c143f3ae
Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>