[SCSI] libfcoe, fcoe: libfcoe NPIV support

[SCSI] libfcoe, fcoe: libfcoe NPIV support

The FIP code in libfcoe needed several changes to support NPIV

1) dst_src_addr needs to be managed per-n_port-ID for FPMA fabrics with NPIV
   enabled.  Managing the MAC address is now handled in fcoe, with some slight
   changes to update_mac() and a new get_src_addr() function pointer.

2) The libfc elsct_send() hook is used to setup FCoE specific response
   handlers for FIP encapsulated ELS exchanges.  This lets the FCoE specific
   handling know which VN_Port the exchange is for, and doesn't require
   tracking OX_IDs.  It might be possible to roll back to the full FIP frame
   in these, but for now I've just stashed the contents of the MAC address
   descriptor in the skb context block for later use.  Also, because
   fcoe_elsct_send() just passes control on to fc_elsct_send(), all transmits
   still come through the normal frame_send() path.

3) The NPIV changes added a mutex hold in the keep alive sending, the lport
   mutex is protecting the vport list.  We can't take a mutex from a timer,
   so move the FIP keep alive logic to the link work struct.

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>