chelsio: misc cleanups in sge

- duplicated code in sge::free_cmdQ_buffers ;
- NET_IP_ALIGN is already defined in (included) <linux/skbuff.h> ;
- pci_alloc_consistent() returns void * ;
- pci_alloc_consistent() returns a zeroed chunk of memory ;
- early return in restart_tx_queues.

Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>