nvmet_fc: Accept variable pad lengths on Create Association LS

Target validation of the Create Association LS revised to accept any
LS as long as all non-pad data has been received. This allows a (newer)
target to accept the LS from older initiators with varying pad lengths.

Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>