selftests/net: update .gitignore with newly added tests

Update .gitignore with newly added tests:
	tools/testing/selftests/net/af_unix/test_unix_oob
	tools/testing/selftests/net/gro
	tools/testing/selftests/net/ioam6_parser
	tools/testing/selftests/net/toeplitz

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>