Align locking usage when touching device address with rest
of the kernel. Lock the bottom half when doing so using
netif_addr_lock_bh.

This also solves the following case as reported by lockdep:
	CPU0                    CPU1
	----                    ----
lock(_xmit_INFINIBAND);
				local_irq_disable();
				lock(&(&mc->mca_lock)->rlock);
				lock(_xmit_INFINIBAND);
<Interrupt>
lock(&(&mc->mca_lock)->rlock);

*** DEADLOCK ***

Fixes: 492a7e67 ("IB/IPoIB: Allow setting the device address")
Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>