Reland "Upconvert various types to int.", ilbc portion.

This reverts portions of commit cb180976dd0e9672cde4523d87b5f4857478b5e9, which
reverted commit 83ad33a8aed1fb00e422b6abd33c3e8942821c24.  Specifically, the
files in webrtc/modules/audio_coding/codecs/ilbc/ are relanded.

The original commit message is below:

Upconvert various types to int.

Per comments from HL/kwiberg on https://webrtc-codereview.appspot.com/42569004 , when there is existing usage of mixed types (int16_t, int, etc.), we'd prefer to standardize on larger types like int and phase out use of int16_t.

Specifically, "Using int16 just because we're sure all reasonable values will fit in 16 bits isn't usually meaningful in C."

This converts some existing uses of int16_t (and, in a few cases, other types such as uint16_t) to int (or, in a few places, int32_t).  Other locations will be converted to size_t in a separate change.

BUG=none
TBR=kwiberg

Review URL: https://codereview.webrtc.org/1184643002

Cr-Commit-Position: refs/heads/master@{#9423}

webrtc/modules/audio_coding/codecs/ilbc/init_decode.c

@@ -23,7 +23,7 @@
  *  Initiation of decoder instance.
  *---------------------------------------------------------------*/
 
-int16_t WebRtcIlbcfix_InitDecode(  /* (o) Number of decoded samples */
+int WebRtcIlbcfix_InitDecode(  /* (o) Number of decoded samples */
     IlbcDecoder *iLBCdec_inst,  /* (i/o) Decoder instance */
     int16_t mode,  /* (i) frame size mode */
     int use_enhancer) {  /* (i) 1: use enhancer, 0: no enhancer */