wwan: update default connection timeout to 200s

The following merge request in ModemManager introduces a more or less common timeout value for the connection attempts in all plugin and protocol implementations:

mobile-broadband/ModemManager!391 (merged)

The value chosen by default for the steps that may take long to complete in a connection attempt is 180s, and 120s for the steps in the disconnection path.

Until now, every different plugin or protocol had a different timeout value, all of them <= 180s, and with that change in ModemManager, the values are now aligned for all.

Note, though, that this does not mean that a connection attempt will take always less than 180s, as there may be multiple other steps in addition to the one that took the maximum timeout. The value chosen for NetworkManager is a compromise between the new defaults from MM and what the user would expect under e.g. very low quality conditions.