iwlwifi: mac start synchronization issue

This patch fixes a synchronization problem on the 4965 and 3945 with the
mac start callback routine.  The problem is that this function exits BEFORE the
'xxx_alive_start' has completed.  This can lead to a problem if a
subsequent MAC callback attempts to issue a firmware command.

Signed-off-by: Rick Farrington <rickdic@hotmail.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>