MM: There is no support for seperate internet and MMS APNs

Some carriers have two mutually exclusive APNs, one for MMS and one for internet. As it stands now, if a user has a carrier like this, they are unable to use mobile internet and send/receive MMS at the same time.

mmsd-tng does not have support to detect multiple APNs, but is waiting on underlying support from Network Manager to provide support for this.

Modem Manager 1.18 supports multi-plexing APNs, but the maintainer has no access to a carrier network that does this, and as such, as no way to build support for it.