ipmr: Make ipmr_dump() common

Since all the primitive elements used for the notification done by ipmr
are now common [mr_table, mr_mfc, vif_device] we can refactor the logic
for dumping them to a common file.

Signed-off-by: Yuval Mintz <yuvalm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>