Make the qtaguid test more stable

The current qtaguid test some time failed doing the
QtaguidTest.testUidGidCombineMatch test because the fin ack packet can
not reach the kernel soon enough sometime. The kernel will end up
sending fin packet again and break the test. To fix this, the random
generated fin packet will be catched before socket close so it will not
interference with the RST packet.

Test: qtaguid test no longer fail randomly
Bug: 37524657
Change-Id: I373ba2e68e8ab84ce54e39476b6cc4983e139c72