Some Nokia modems only support "MT" as the incoming sms store.
Presumably the modem has some intelligence to pick the right store
depending on the SMS class. This means that oFono must now track
what the current store is, and issue a CPMS, CMGR & CMGD when a
CMTI notification arrives.
Since the PDU line doesn't have a prefix, the parser can get confused
if other unsolicited notifications arrive. There is already explicit
support for unsolicited notifications with PDU, so we use that
instead
- Can receive 7Bit, 8Bit and UCS2 encoded messages
- 8Bit is assumed to be a datagram to a certain port
- Messages with Invalid format are ignored
- Concatenation not yet supported