Fix external loopback failure.

Rx sequence reassembly was incorrect.
Signed-off-by: NDick Kennedy <dick.kennedy@avagotech.com>
Signed-off-by: NJames Smart <james.smart@avagotech.com>
Reviewed-by: NHannes Reinicke <hare@suse.de>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>