Same code is executed in both rxe_param_set_add and rxe_notify functions.
Make one function and call it from both places.

Since both callers already have a rxe object use it directly instead of
deriving it from the net device.
Signed-off-by: NYuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Steve Wise <swise@opengridcomputing.com> 
Reviewed-by: NBart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>