mlxsw: spectrum: Remove RTNL where possible

After introducing the router lock in previous patches and making sure it
protects internal router structures, we no longer need to rely on RTNL
to serialize access to these structures.

Remove RTNL from call sites that no longer require it.

Two calls sites that keep taking the lock are
mlxsw_sp_router_fibmr_event_work() and mlxsw_sp_inet6addr_event_work().
The first calls into ACL code that still assumes RTNL is taken. The
second potentially calls into the FID code that also relies on RTNL.
Removing RTNL from these two call sites is the subject of future work.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>