Fix the asterisk sounds url mirror mechanism

Check the asterisk sounds url availability. If it is not available
(sometimes asterisk server is down and we could not build our asterisk
fork) then use the iopsys mirror url instead to build the asterisk sounds.

sounds/Makefile

@@ -22,8 +22,12 @@ MOH_DIR:=$(DESTDIR)$(ASTDATADIR)/moh
 CORE_SOUNDS_VERSION:=1.6.1
 EXTRA_SOUNDS_VERSION:=1.5.2
 MOH_VERSION:=2.03
+AST_SERVER_AVAILABLE:=$(shell curl --head --silent --fail http://downloads.asterisk.org/pub/telephony/sounds/releases 2> /dev/null)
+ifneq ($(AST_SERVER_AVAILABLE),)
 SOUNDS_URL:=http://downloads.asterisk.org/pub/telephony/sounds/releases
-SOUNDS_URL_MIRROR:=https://download.iopsys.eu/iopsys/mirror/asterisk/sounds/releases
+else
+SOUNDS_URL:=https://download.iopsys.eu/iopsys/mirror/asterisk/sounds/releases
+endif
 MCS:=$(subst -EN-,-en-,$(MENUSELECT_CORE_SOUNDS))
 MCS:=$(subst -EN_AU-,-en_AU-,$(MCS))
 MCS:=$(subst -EN_GB-,-en_GB-,$(MCS))
@@ -119,9 +123,6 @@ else
 	if test ! -f $$@ && test ! -f "$(1)$(if $(3),/$(3),)/.$$(subst .tar.gz,,$$@)"; then \
 	  $$(DOWNLOAD) $$(SOUNDS_URL)/$$@; \
 	fi
-	if test ! -f $$@ && test ! -f "$(1)$(if $(3),/$(3),)/.$$(subst .tar.gz,,$$@)"; then \
-	  $$(DOWNLOAD) $$(SOUNDS_URL_MIRROR)/$$@; \
-	fi
 endif
 endef # sound_format_lang_rule