Increase buffer size because the header itself can be larger than 8192

(largest size according to spec: 64k). Fixes playback of
mmsh://a1635.v24937.c2493.g.vm.akamaistream.net/7/1635/2493/v0001/premrad.download.akamai.com/2493/premiere_rock_report/Country_Report.wma

Patch by Zhentan Feng <spyfeng gmail com>.

Originally committed as revision 26047 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mms.h

@@ -39,7 +39,7 @@ typedef struct {
 
     /** Buffer for incoming packets. */
     /*@{*/
-    uint8_t in_buffer[8192];             ///< Buffer for incoming packets.
+    uint8_t in_buffer[65536];            ///< Buffer for incoming packets.
     uint8_t *read_in_ptr;                ///< Pointer for reading from incoming buffer.
     int remaining_in_len;                ///< Reading length from incoming buffer.
     /*@}*/