Use White List for direct connection establishment to multiple devices

Currently, we implement GAP Direct Connect procedure exactly as the spec
says: we attempt connection to just one device.

This means that an app doing Direct Connection can take over the ability
to establish connections, and if it repeats the request, can cause other
devices to not connect.

From now on, we will use White List for both Background and Direct
connections. When there is at least one direct connection, we will
increase the scan parameters used for connection.

Bug: 112827989
Test: added unittests, also sl4a GattConnectTest
Change-Id: Ic0b2f631e3c84d5e8e0f4683b0148f031bfd5639