Bug 872983 - event.settingValue in mozSettings.onsettingchange gives wrong value. r=fabrice
Bug 875390 - Add MMSC and/or MMS Proxy specific host routes via MMS APN. r=vyang

MMS sending has been failing because often the default network route was
not going through the MMS APN. This commit adds specific host route via
the correct network interface for either MMSC or MMS proxy depending on
the carrier information. We also perform DNS resolution to cope with
MMSC/proxy that are using FQDN.