net: ipv6: ping: Use socket mark in routing lookup

Change-Id: I31e1a6912e5a91a1448cb2d58bcb027953ed2a60
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>