BugLink: http://bugs.launchpad.net/bugs/1172151

Need to set wapf to 4 for ASUSTeK COMPUTER INC. X75A, so that
user can toggle wifi function through function key correctly.
Signed-off-by: NAceLan Kao <acelan.kao@canonical.com>
Signed-off-by: NMatthew Garrett <matthew.garrett@nebula.com>