tests: fix broken test test_gtpu.py TestGtpuUDP

tests: fix broken test test_gtpu.py TestGtpuUDP

Test failing due to call to super.tearDown in setUp.

==============================================================================
FAIL: test UDP ports
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Traceback (most recent call last):
  File "/vpp/test/test_gtpu.py", line 77, in test_udp_port
    self._check_udp_port_ip4(False)
  File "/vpp/test/test_gtpu.py", line 48, in _check_udp_port_ip4
    self.assertEqual(err, self.ip4_err + 1)
AssertionError: 0L != 1

Type: fix

Change-Id: Iec4ef5edd3ee11bcd962b77cc8159dee9cb15687
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>