Relay cause of hangup on SRTP failure

We hangup the channel after receiving 10 SRTP packets in a row with a
bad auth tag or that are replayed.  Prior to this commit we were
indicating a normal clearing.  When doing interop and looking first at
packet traces, this made freeswitch's behavior look surprising.  With
this commit we'll indicate more loudly what's happening.

src/include/switch_types.h

@@ -1968,7 +1968,8 @@ typedef enum {
 	SWITCH_CAUSE_GATEWAY_DOWN = 609,
 	SWITCH_CAUSE_INVALID_URL = 610,
 	SWITCH_CAUSE_INVALID_PROFILE = 611,
-	SWITCH_CAUSE_NO_PICKUP = 612
+	SWITCH_CAUSE_NO_PICKUP = 612,
+	SWITCH_CAUSE_SRTP_READ_ERROR = 613
 } switch_call_cause_t;
 
 typedef enum {