cxgb4i: set the initial sequence number

set the initial sequence number so the 1st byte of payload is aligned on
the 8-byte boundary.

Signed-off-by: Karen Xie <kxie@chelsio.com>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Odin.com>