Use audio_channel_mask_t more consistently

In AudioRecord::getMinFrameCount() and AudioSystem::getInputBufferSize(),
input parameter is channel mask instead of channel count.

Change-Id: I22a1c492113f3e689173c5ab97b2567cff3abe2b
diff --git a/jni/rtp/AudioGroup.cpp b/jni/rtp/AudioGroup.cpp
index 673a650..1579e6a 100644
--- a/jni/rtp/AudioGroup.cpp
+++ b/jni/rtp/AudioGroup.cpp
@@ -790,7 +790,7 @@
     if (AudioTrack::getMinFrameCount(&output, AUDIO_STREAM_VOICE_CALL,
         sampleRate) != NO_ERROR || output <= 0 ||
         AudioRecord::getMinFrameCount(&input, sampleRate,
-        AUDIO_FORMAT_PCM_16_BIT, 1) != NO_ERROR || input <= 0) {
+        AUDIO_FORMAT_PCM_16_BIT, AUDIO_CHANNEL_IN_MONO) != NO_ERROR || input <= 0) {
         ALOGE("cannot compute frame count");
         return false;
     }