Use aggressive initial connection params

This CL makes the stack use aggressive initial connection
parameters when there are less than 2 ongoing ACL connections.

Bug: 308483803
Bug: 378595485
Flag: com.android.bluetooth.flags.initial_conn_params_p1
Test: atest LeImplTest
Test: atest GattClientTest
Test: Manual, checked aggressive params are used for first connection,
      and relaxed params are used from the third connection.
Test: Manual, checked that paramters are relaxed after service
      discovery. Also for the case when the service discovery is
      skipped.
Test: Manual, made GATT connection while music is playing via A2DP/ASHA.
      The music was continously playing while service discovery.
Test: Manual, had a Wifi traffic and phone call with HFP/ASHA.
      The phone call has no noticable sound errors.
Change-Id: Idd8cac01f67e4dd797487fad87781fddb5ce73d3