selftests: forwarding: mirror_gre_vlan_bridge_1q: Fix tunnel name

The "ip6gretap" in the test name refers to the tunnel device type that
the test is supposed to be testing. However test_ip6gretap_forbidden()
tests, due to a typo, a gretap tunnel. Fix the typo.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/forwarding/mirror_gre_vlan_bridge_1q.sh

@@ -108,7 +108,7 @@ test_gretap_forbidden()
 
 test_ip6gretap_forbidden()
 {
-	test_span_gre_forbidden gt4 "mirror to ip6gretap"
+	test_span_gre_forbidden gt6 "mirror to ip6gretap"
 }
 
 test_all()