selftests: forwarding: Add some missing configuration symbols

For the forwarding selftests to work, we need network namespaces when
using veth/vrf otherwise ping/ping6 commands like these:

ip vrf exec vveth0 /bin/ping 192.0.2.2 -c 10 -i 0.1 -w 5

will fail because network namespaces may not be enabled.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/forwarding/config

@@ -10,3 +10,5 @@ CONFIG_NET_CLS_FLOWER=m
 CONFIG_NET_SCH_INGRESS=m
 CONFIG_NET_ACT_GACT=m
 CONFIG_VETH=m
+CONFIG_NAMESPACES=y
+CONFIG_NET_NS=y