Send a dbus reply only if requested by the caller

Send a dbus reply only if requested by the caller

wpa_supplicant should not send a dbus reply as response to a method call
if no reply was requested by the caller. Sending a reply even if not
requested is basically no problem but triggers dbus warnings like the
one below.

Feb  9 07:31:23 linux-gvjr dbus-daemon: Rejected send message, 2 matched
rules; type="error", sender=":1.129" (uid=0 pid=30228
comm="/usr/sbin/wpa_supplicant -c /etc/wpa_supplicant/wp")
interface="(unset)" member="(unset)" error
name="fi.epitest.hostap.WPASupplicant.InvalidInterface"
requested_reply=0 destination=":1.128" (uid=0 pid=30226
comm="/usr/sbin/NetworkManager "))

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>