selftests: add few test cases for tap driver

Few test cases related to the fix for 924a9bc3:
"net: check if protocol extracted by virtio_net_hdr_set_proto is correct"

Need test for the case when a non-standard packet (GSO without NEEDS_CSUM)
sent to the tap device causes a BUG check in the tap driver.
Signed-off-by: Cezar Bulinaru <cbulinaru@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/.gitignore

@@ -39,3 +39,4 @@ toeplitz
 tun
 cmsg_sender
 unix_connect
+tap
\ No newline at end of file

tools/testing/selftests/net/Makefile

@@ -57,7 +57,7 @@ TEST_GEN_FILES += ipsec
 TEST_GEN_FILES += ioam6_parser
 TEST_GEN_FILES += gro
 TEST_GEN_PROGS = reuseport_bpf reuseport_bpf_cpu reuseport_bpf_numa
-TEST_GEN_PROGS += reuseport_dualstack reuseaddr_conflict tls tun
+TEST_GEN_PROGS += reuseport_dualstack reuseaddr_conflict tls tun tap
 TEST_GEN_FILES += toeplitz
 TEST_GEN_FILES += cmsg_sender
 TEST_GEN_FILES += stress_reuseport_listen