base-modem: explicitly say if NET or TTY data ports are supported
A modem that creates exclusively bearer objects that work with NET ports (e.g. all QMI or MBIM modems) must not add any TTY port in the list of data ports.
A modem that creates exclusively bearer objects that work with TTY ports (e.g. the generic modem) must not add any NET port in the list of data ports.
A modem that may use both TTY and NET ports should add all in the list of data ports.
Fixes #324 (closed) Fixes #329 (closed)