bonding: alb: remove curr_slave_lock

First in rlb_teach_disabled_mac_on_primary() it's okay to remove
curr_slave_lock as all callers except bond_alb_monitor() already hold
RTNL, and in case bond_alb_monitor() is executing we can at most have a
period with bad throughput (very unlikely though).
In bond_alb_monitor() it's okay to remove the read_lock as the slave
list is walked with RCU and the worst that could happen is another
transmitter at the same time and thus for a period which currently is 10
seconds (bond_alb.h: BOND_ALB_LP_TICKS).
And bond_alb_handle_active_change() is okay because it's always called
with RTNL. Removed the ASSERT_RTNL() because it'll be inserted in the
parent function in a following patch.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>