rtp_engine: Allow more than 32 dynamic payload types.

Since adding all remaining rates of Signed Linear (ASTERISK-24274) and SILK
(Gerrit 3136), only one RTP Payload Type is left in the dynamic range (96-127).
RFC 3551 section 3 allows to reassign other ranges. Consequently, when the
dynamic range is exhausted, you can go for "rtp_pt_dynamic = 35" (or 0) in
asterisk.conf. This enables the range 35-63 (or 0-63) giving room for another
29 (or 64) payload types.

ASTERISK-26311 #close

Change-Id: I7bc96ab764bc30098a178b841cbf7146f9d64964

include/asterisk/options.h

@@ -155,6 +155,8 @@ extern int dahdi_chan_name_len;
 
 extern int ast_language_is_prefix;
 
+extern unsigned int ast_option_rtpptdynamic;
+
 #if defined(__cplusplus) || defined(c_plusplus)
 }
 #endif

include/asterisk/rtp_engine.h

@@ -84,6 +84,9 @@ extern "C" {
 /*! First dynamic RTP payload type */
 #define AST_RTP_PT_FIRST_DYNAMIC 96
 
+/*! Last reassignable RTP payload type */
+#define AST_RTP_PT_LAST_REASSIGN 63
+
 /*! Maximum number of generations */
 #define AST_RED_MAX_GENERATION 5