[SCSI] libfcoe: Handle duplicate critical descriptors

As per FC-BB-5 rev 2, section 7.8.6.2, malformed FIP frame shall be
discarded. Drop discovery adv, ELS and CLV's with duplicate critical
descriptors.

[Resending after incorporating Joe's review comments]

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