constify ast_state2str() and note it is not reentrant.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@48477 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/channel.h

@@ -1060,7 +1060,7 @@ int ast_str2cause(const char *name) attribute_pure;
  * Give a name to a state 
  * Returns the text form of the binary state given
  */
-char *ast_state2str(enum ast_channel_state);
+const char *ast_state2str(enum ast_channel_state);
 
 /*! Gives the string form of a given transfer capability */
 /*!

main/channel.c

@@ -516,8 +516,10 @@ int ast_str2cause(const char *name)
 	return -1;
 }
 
-/*! \brief Gives the string form of a given channel state */
-char *ast_state2str(enum ast_channel_state state)
+/*! \brief Gives the string form of a given channel state.
+	\note This function is not reentrant.
+ */
+const char *ast_state2str(enum ast_channel_state state)
 {
 	char *buf;