Added NET_CAPABILITY_MMTEL to indicate a network support MMTEL (Multimedia telephony). This is for IMS service to request an IMS network that supports voice or PS (VoPS for 4G, VoNR for 5G). This was previously submitted as aosp/1927841, but which got reverted due to breaking the mainline build, which uses the pre-built module. Bug: 210774375 Test: atest ConnectivityServiceTest Change-Id: If8b691ff4999a4dbf54e7567d9ca74d743dc5ded