[SCSI] libfcoe: Avoid hang when receiving non-critical descriptors

Avoid infinite loop while processing FIP ELS or discovery
advertisement with non-critical descriptors.

Signed-off-by: Bhanu Prakash Gollapudi <bprakash@broadcom.com>
Acked-by: Joe Eykholt <jeykholt@cisco.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>