asterisk-chan-dongle: overhaul

asterisk-chan-dongle: overhaul

- Make the Makefile use BUILD_VARIANT so the package can be built for
  different Asterisk versions. This is also the reason why the folder is
  renamed from asterisk-11.x-chan-dongle to asterisk-chan-dongle.
- Change source URI from upstream to the fork of wdoekes. Upstream
  doesn't update the repo anymore, wdoekes does.
- Remove dep on libiconv-full, make the package use toolchain's iconv
  (compile-tested with musl).
- Drop patches that are already upstream.
- Update flags.

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