Resolve a few issues with cell info notifications

See merge request mer-core/ofono!286

1. Disable notifications from modem on unsibscribe
2. Made all signals unicast
3. Fixed a memory leak

1. Exposed D-Bus clients list to plugin as ofono_dbus_clients
2. Signal has to be properly declared, otherwise it's not emitted
3. Added missing unit tests

Disable cell info updates when no one listens for them

See merge request mer-core/ofono!274

Expose P-CSCF address(es) over D-Bus

See merge request mer-core/ofono!285

Don't limit MTU for non-MMS contexts

See merge request mer-core/ofono!284

Larger MTU means better throughput, and the original problem for which
this workaround was implemented was specific to MMS. There's no reason
to limit MTU for other data connections.

Also optimized reporting of DNS addresses by not setting empty lists.
If nothing else, that slightly reduces the amount of D-Bus traffic.

It worked only because aid was the first field in the struct.

Implement org.ofono.SimAuthentication interface

See merge request mer-core/ofono!283

They can be shorter than 16 bytes.

Empty path never works and some RILs/modems don't like it so much
that it causes a reset.

Add a new org.nemomobile.ofono.CellInfo.Unsubscribe method. If it is called
ofono excludes the client from cell info consumers. The updates will be
disabled if no one client left.

[ril] Use ofono_sim_read_path() in case of reading EFpbr from USIM. Fixes JB#54420

See merge request mer-core/ofono!282

There is an issue when some of the Mediatek modems do not accept empty
path to the EFpbr file on the USIM and do reset themselves.
This fix appends usim_path to the GET DATA command when it comes to
exporting phonebook from SIM card and prevents crashes like described
one.

The intent here was to find the contents of the 3 low order bits
according to Table 11-5 in ETSI 102.221.  However, the mask ended up
only grabbing the contents of the 2 low order bits.

Session has to be open in order to have a valid session_id

Otherwise open_channel won't be called again after a failure.

Keep track of P-CSCF address

See merge request mer-core/ofono!281

And use IMS data profile for IMS data calls.

Miscellaneous mobile data issues

See merge request mer-core/ofono!280

grilio_channel_retry_request() returns FALSE if the request is pending,
i.e. has been submitted but there was no reply yet. In that case, in
order to retry right away, we need to cancel the already submitted
request (and ignore the reply when it arrives) and resubmit a fresh
new one.

Sumbit a pending request from the DBus queue

See merge request mer-core/ofono!279

Currently, the DBus queue stops working after an asynchronous request
has been completed while another request is pending. This commit adds
__ofono_dbus_queue_submit_next(), which fires a pending request after
the previous one completes.

Get rid of unwanted retries on manual network connection

See merge request !278

There is an issue when network operators return "allowed" flag no matter
which SIM card you are using currently. In that case, when user tries to
manually connect to such networks, it takes too long to have 2 (by
default) retries until device will get back to its home network.
So the solution is not to set additional retries to the
RIL_REQUEST_SET_NETWORK_SELECTION_MANUAL request, as it has been done
in RILJ.

Register HandsfreeAudioManager straight away at startup

See merge request mer-core/ofono!277

To ensure that all D-Bus objects which should be available straight
after startup are there when the first incoming D-Bus call arrives.