asterisk-chan-dongle: adapt BUILD_NLS handling

asterisk-chan-dongle: adapt BUILD_NLS handling

openwrt recently stopped using libiconv-stub in the BUILD_NLS=n case.
Instead the libc's iconv has to be used.

This commit changes the iconv include path passed to
asterisk-chan-dongle for the BUILD_NLS=n case to
$(TOOLCHAIN_DIR)/include. That's where musl and glibc store iconv.h.

Also, the patch 200-fix-iconv-detection.patch gets replaced with a sed
script that only runs in the BUILD_NLS=y case.

And finally, $(AUTORELEASE) is added.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>