Fix lockup in audio flinger threadbase setParameters.

The function checkForNewParameters_l() is called with the ThreadBase mutex mLock locked. In the case where the parameter change implies
an audio parameter modification (e.g. sampling rate) the function sendConfigEvent() is called which tries to lock mLock creating a deadlock.

The fix consists in creating a function equivalent to sendConfigEvent() that must be called with mLock locked and does not lock mLock.

Also added the possibility to have more than one set parameter request pending.