UBUNTU: SAUCE: selftests: net: fix "from" match test in fib_rule_tests.sh

Fix the IPv4 address of the dummy0 interface and ensure that ip_forward
is enabled in the network space to get a valid response when checking
for routes between the gateway and other hosts.

Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>

tools/testing/selftests/net/fib_rule_tests.sh

@@ -87,6 +87,8 @@ setup()
 	$IP address add $DEV_ADDR/24 dev dummy0
 	$IP -6 address add $DEV_ADDR6/64 dev dummy0
 
+	ip netns exec testns sysctl -w net.ipv4.ip_forward=1
+
 	set +e
 }