clang compiler warnings: Fix -Wunused-function; make inline function static

This patch fixes clang compilers warnings for unused functions. Specifically:
 * channels/chan_iax2: removed user_ref function
 * main/dsp.c: removed goertzel_update function
 * main/config.c: made variable_list_switch static

Review: https://reviewboard.asterisk.org/r/4527

ASTERISK-24917
Reported by: dkdegroot
patches:
  rb4527.patch submitted by dkdegroot (License 6600)
........

Merged revisions 433678 from http://svn.asterisk.org/svn/asterisk/branches/11
........

Merged revisions 433680 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@433681 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_iax2.c

@@ -2014,11 +2014,6 @@ static struct iax2_user *find_user(const char *name)
 {
 	return ao2_find(users, name, OBJ_KEY);
 }
-static inline struct iax2_user *user_ref(struct iax2_user *user)
-{
-	ao2_ref(user, +1);
-	return user;
-}
 
 static inline struct iax2_user *user_unref(struct iax2_user *user)
 {

main/config.c

@@ -71,7 +71,7 @@ static char *extconfig_conf = "extconfig.conf";
 
 static struct ao2_container *cfg_hooks;
 static void config_hook_exec(const char *filename, const char *module, const struct ast_config *cfg);
-inline struct ast_variable *variable_list_switch(struct ast_variable *l1, struct ast_variable *l2);
+static inline struct ast_variable *variable_list_switch(struct ast_variable *l1, struct ast_variable *l2);
 static int does_category_match(struct ast_category *cat, const char *category_name, const char *match);
 
 /*! \brief Structure to keep comments for rewriting configuration files */
@@ -614,7 +614,7 @@ struct ast_variable *ast_variable_browse(const struct ast_config *config, const
 	return (cat) ? cat->root : NULL;
 }
 
-inline struct ast_variable *variable_list_switch(struct ast_variable *l1, struct ast_variable *l2)
+static inline struct ast_variable *variable_list_switch(struct ast_variable *l1, struct ast_variable *l2)
 {
     l1->next = l2->next;
     l2->next = l1;

main/dsp.c

@@ -339,16 +339,6 @@ static inline void goertzel_sample(goertzel_state_t *s, short sample)
 	}
 }
 
-static inline void goertzel_update(goertzel_state_t *s, short *samps, int count)
-{
-	int i;
-
-	for (i = 0; i < count; i++) {
-		goertzel_sample(s, samps[i]);
-	}
-}
-
-
 static inline float goertzel_result(goertzel_state_t *s)
 {
 	goertzel_result_t r;