modemmanager: add option to force connection

modemmanager: add option to force connection

This commit improves the automatic reconnect logic. If the modem cannot
establish a connection, for example due to poor reception, the
proto_block_restart prevents the interface from trying to reconnect.
To enforce the connection, this commit adds a new option that allows the
system to attempt to establish a connection indefinitely.

Signed-off-by: Oliver Sedlbauer <redacted>