scsi: lpfc: Fix RSCN timeout due to incorrect gidft counter

In configs with a large number of initiators in the same zone (>250), RSCN
timeouts are seen when creating or deleting vports:

   lpfc 0000:07:00.1: 5:(0):0231 RSCN timeout Data: x0 x3

During RSCN processing driver issues GID_FT command to nameserver. A
counter for number of simultaneous GID_FT commands is maintained (an
unsigned value). The counter is incremented when the GID_FT is issued.  If
the GID_FT command fails for some reason the driver retries the GID_FT from
the completion call back. But the counter was decremented before the retry
was issued.  When the second GID_FT completes, the callback again tries to
decrement the counter, possibly wrapping to a very large non-zero value,
which causes the RSCN cleanup code to not execute. Thus the RSCN timeout
failure.

Do not decrement the counter on a retry. Also add defensive checks to
ensure the counter is not decremented if already zero.

Link: https://lore.kernel.org/r/20200803210229.23063-4-jsmart2021@gmail.com


Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>