Don't disconnect an A2DP device when connecting to same device

Don't disconnect an A2DP device when connecting to same device

When processing a connect request for an A2DP device, Settings
would trigger a disconnect request for all A2DP devices that
have state of CONNECTED, CONNECTING or DISCONNECTING, including
eventually the device we are connecting to.
This could create timing-related issues, and is not necessary.
Now we explicitly check to avoid disconnecting the device we are
connecting to.

Test: Manual A2DP testing with a phone and wireless headsets
Bug: 32688022
Change-Id: I572dd87c071829b734513c4b928a4d65fe539520