add columns of Carrier about MVNO

To recognize MVNO, use new fields, MVNO_MATCH_DATA and MVNO_TYPE
(SPN, IMSI, GID(Group Identifier Level 1)).

Bug: 8143480
Change-Id: Idfa06c6f39a2c15ff4f0815724823f44b76ac819
Telephony: Return 'null' when SubscriberId and Line1Number are unavailable

Return 'null' instead of "" (empty string) when Subscriber Id and
Line1Number are unavailable. This confirms to the definition of the
public API.

Bug: 8284793
Change-Id: Ie6395623cf413d51f6e10316aded71e2eaf5592c