connection_manager: one method for direct connect establishment

Currently in stack we have two methods for establishing direct conenct:
* create_le_connection
* direct_connect_add

create_le_connection is making direct call to GD to schedule
direct connection. It relies on timer in GD to stop the attempt after 30
seconds. It doesn't track which app requested direct connect, so it
can't properly cancel direct connect if request was made from multiple
clients, and just one cancels it.

direct_connect_add keeps track of clients that made a request, but it
works only if it's the only function used to establish direct connect.
If create_le_connection, or GD is called directly, the counting breaks.

The logic for scheduling/canceling direct connect using
direct_connect_add was already tested in unit tests, but when
create_le_connection is in use through the stack, those tests don't
reflect the stack behavior.

In create_le_connection, some extra address checks and lookups were
added to prevent stack from attempting direct connect to targetted
announcements. These are copied to direct_connect_add.

Test: atest net_test_conn_multiplexing
Bug: 372202918
Flag: EXEMPT, covered under unittests
Change-Id: I76b2a4d5012fe473aa01a3df89e7b4794689a1d6