avconv: rename InputStream.opts to InputStream.decoder_opts

This makes it more clear what is this variable for exactly.
diff --git a/avconv_opt.c b/avconv_opt.c
index ae6c48b..22f598e 100644
--- a/avconv_opt.c
+++ b/avconv_opt.c
@@ -492,7 +492,7 @@
         }
 
         ist->dec = choose_decoder(o, ic, st);
-        ist->opts = filter_codec_opts(o->g->codec_opts, ist->st->codec->codec_id, ic, st, ist->dec);
+        ist->decoder_opts = filter_codec_opts(o->g->codec_opts, ist->st->codec->codec_id, ic, st, ist->dec);
 
         switch (dec->codec_type) {
         case AVMEDIA_TYPE_VIDEO:
@@ -754,7 +754,7 @@
     unused_opts = strip_specifiers(o->g->codec_opts);
     for (i = f->ist_index; i < nb_input_streams; i++) {
         e = NULL;
-        while ((e = av_dict_get(input_streams[i]->opts, "", e,
+        while ((e = av_dict_get(input_streams[i]->decoder_opts, "", e,
                                 AV_DICT_IGNORE_SUFFIX)))
             av_dict_set(&unused_opts, e->key, NULL, 0);
     }