selftests: forwarding: gre_multipath: Enable IPv4 forwarding

The test did not enable IPv4 forwarding during its setup phase, which
causes the test to fail on machines where IPv4 forwarding is disabled.

Fixes: 54818c4c ("selftests: forwarding: Test multipath tunneling")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reported-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Tested-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -187,12 +187,16 @@ setup_prepare()
 	sw1_create
 	sw2_create
 	h2_create
+
+	forwarding_enable
 }
 
 cleanup()
 {
 	pre_cleanup
 
+	forwarding_restore
+
 	h2_destroy
 	sw2_destroy
 	sw1_destroy