[SCSI] fcoe: Don't hold rtnl_mutex in fcoe_update_src_mac

The rtnl_mutex was held to protect calls to dev_uc_add
and dev_uc_del. Holding rtnl is not required as those
functions make use of the netif_addr_lock* API to
protect the MAC changing.

This change fixes the following regression by removing
the rtnl usage when fcoe_update_src_mac is called.

https://bugzilla.kernel.org/show_bug.cgi?id=42918

the existing dependency chain (in reverse order) is:

-> #1 (&fip->ctlr_mutex){+.+...}:
       [<c1091f70>] lock_acquire+0x80/0x1b0
       [<c147655d>] mutex_lock_nested+0x6d/0x340
       [<f8970c32>] fcoe_ctlr_link_up+0x22/0x180 [libfcoe]
       [<f894620e>] fcoe_create+0x47e/0x6e0 [fcoe]
       [<f8973dd3>] fcoe_transport_create+0x143/0x250 [libfcoe]
       [<c10527e0>] param_attr_store+0x30/0x60
       [<c1052696>] module_attr_store+0x26/0x40
       [<c11a201e>] sysfs_write_file+0xae/0x100
       [<c11449df>] vfs_write+0x8f/0x160
       [<c1144cbd>] sys_write+0x3d/0x70
       [<c147a0c4>] syscall_call+0x7/0xb

-> #0 (rtnl_mutex){+.+.+.}:
       [<c109164b>] __lock_acquire+0x140b/0x1720
       [<c1091f70>] lock_acquire+0x80/0x1b0
       [<c147655d>] mutex_lock_nested+0x6d/0x340
       [<c13a10c4>] rtnl_lock+0x14/0x20
       [<f89445ac>] fcoe_update_src_mac+0x2c/0xb0 [fcoe]
       [<f8971712>] fcoe_ctlr_timer_work+0x712/0xb60 [libfcoe]
       [<c104fb69>] process_one_work+0x179/0x5d0
       [<c10502f1>] worker_thread+0x121/0x2d0
       [<c10550ed>] kthread+0x7d/0x90
       [<c1481a82>] kernel_thread_helper+0x6/0x10

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&fip->ctlr_mutex);
                               lock(rtnl_mutex);
                               lock(&fip->ctlr_mutex);
  lock(rtnl_mutex);

 *** DEADLOCK ***
Signed-off-by: Robert Love <robert.w.love@intel.com>
Tested-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/fcoe/fcoe.c

@@ -536,13 +536,11 @@ static void fcoe_update_src_mac(struct fc_lport *lport, u8 *addr)
 	struct fcoe_port *port = lport_priv(lport);
 	struct fcoe_interface *fcoe = port->priv;
 
-	rtnl_lock();
 	if (!is_zero_ether_addr(port->data_src_addr))
 		dev_uc_del(fcoe->netdev, port->data_src_addr);
 	if (!is_zero_ether_addr(addr))
 		dev_uc_add(fcoe->netdev, addr);
 	memcpy(port->data_src_addr, addr, ETH_ALEN);
-	rtnl_unlock();
 }
 
 /**