cxgb3: Wait longer for control packets on initialization

In some Power7 platforms, when using VIOS (Virtual I/O Server), we
need to wait longer for control packets to finish transfer during
initialization.
Without this change, initialization may fail prematurely.

Signed-off-by: Wen Xiong <wenxiong@us.ibm.com>
Signed-off-by: Andre Detsch <adetsch@br.ibm.com>
Acked-by: Divy Le Ray <divy@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>