In order not to hold RTNL for long periods of time we're going to dump
the FIB tables using RCU.

Convert the FIB notification chain to be atomic, as we can't block in
RCU critical sections.
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Signed-off-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>