[SCSI] fcoe: reduce contention for fcoe_rx_list lock [v2]

There is potentially lots of contention for the rx_list_lock.  On a cpu that is
receiving lots of fcoe traffic, the softirq context has to add and release the
lock for every frame it receives, as does the receiving per-cpu thread.  We can
reduce this contention somewhat by altering the per-cpu threads loop such that
when traffic is detected on the fcoe_rx_list, we splice it to a temporary list.
In this way, we can process multiple skbs while only having to acquire and
release the fcoe_rx_list lock once.

[ Braces around single statement while loop removed by Robert Love
  to satisfy checkpath.pl. ]

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Vasu Dev <vasu.dev@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>