selftests/net: Add missing config options for PMTU tests

PMTU tests in pmtu.sh need support for VTI, VTI6 and dummy
interfaces: add them to config file.
Reported-by: NNaresh Kamboju <naresh.kamboju@linaro.org>
Fixes: d1f1b9cb ("selftests: net: Introduce first PMTU test")
Signed-off-by: NStefano Brivio <sbrivio@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/testing/selftests/net/config

@@ -7,3 +7,8 @@ CONFIG_NET_L3_MASTER_DEV=y
 CONFIG_IPV6=y
 CONFIG_IPV6_MULTIPLE_TABLES=y
 CONFIG_VETH=y
+CONFIG_INET_XFRM_MODE_TUNNEL=y
+CONFIG_NET_IPVTI=y
+CONFIG_INET6_XFRM_MODE_TUNNEL=y
+CONFIG_IPV6_VTI=y
+CONFIG_DUMMY=y