selftests: fib_rule_tests: enable forwarding before ipv4 from/iif test

As all the testing addresses are in the same subnet and egress device ==
ingress device. We need enable forwarding to get the route entry.

Also disable rp_filer separately as some distributions enable it in
startup scripts.

Fixes: 65b2b493 ("selftests: net: initial fib rule tests")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/fib_rule_tests.sh

@@ -186,8 +186,13 @@ fib_rule4_test()
 	match="oif $DEV"
 	fib_rule4_test_match_n_redirect "$match" "$match" "oif redirect to table"
 
+	# need enable forwarding and disable rp_filter temporarily as all the
+	# addresses are in the same subnet and egress device == ingress device.
+	ip netns exec testns sysctl -w net.ipv4.ip_forward=1
+	ip netns exec testns sysctl -w net.ipv4.conf.$DEV.rp_filter=0
 	match="from $SRC_IP iif $DEV"
 	fib_rule4_test_match_n_redirect "$match" "$match" "iif redirect to table"
+	ip netns exec testns sysctl -w net.ipv4.ip_forward=0
 
 	match="tos 0x10"
 	fib_rule4_test_match_n_redirect "$match" "$match" "tos redirect to table"