selftests: mptcp: turn rp_filter off on each NIC

To turn rp_filter off we should:

  echo 0 > /proc/sys/net/ipv4/conf/default/rp_filter

and

  echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter

before NIC created.
Co-developed-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NPaolo Abeni <pabeni@redhat.com>
Signed-off-by: NYonglong Li <liyonglong@chinatelecom.cn>
Signed-off-by: NMat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/testing/selftests/net/mptcp/simult_flows.sh

@@ -60,6 +60,8 @@ setup()
 	for i in "$ns1" "$ns2" "$ns3";do
 		ip netns add $i || exit $ksft_skip
 		ip -net $i link set lo up
+		ip netns exec $i sysctl -q net.ipv4.conf.all.rp_filter=0
+		ip netns exec $i sysctl -q net.ipv4.conf.default.rp_filter=0
 	done
 
 	ip link add ns1eth1 netns "$ns1" type veth peer name ns2eth1 netns "$ns2"
@@ -80,7 +82,6 @@ setup()
 
 	ip netns exec "$ns1" ./pm_nl_ctl limits 1 1
 	ip netns exec "$ns1" ./pm_nl_ctl add 10.0.2.1 dev ns1eth2 flags subflow
-	ip netns exec "$ns1" sysctl -q net.ipv4.conf.all.rp_filter=0
 
 	ip -net "$ns2" addr add 10.0.1.2/24 dev ns2eth1
 	ip -net "$ns2" addr add dead:beef:1::2/64 dev ns2eth1 nodad