alsa_sound: fix for SIP call mute issue.

-Mute VOIP through audio path is not supported by kernel,
 so calling setVoipMicMute() to disable ""Voip Tx Mute"" fails
-Mute VOIP by cleanning buffers read if setMicMute is set
-Remove mVoipMicMute and use mMicMute for voice and VOIP

Bug: 7213748
Change-Id: I62be8456447425cbd1521083782802effcb6d326
Signed-off-by: Iliyan Malchev <malchev@google.com>