kamailio-5.x: bump to 5.2.1

kamailio-5.x: bump to 5.2.1

- bump to 5.2.1
- drops sources.openwrt.org from PKG_SOURCE_URL because this mirror is
  meant as last resort
- adds six new modules (app_python3 marked @BROKEN - doesn't compile
  yet)
- 050-fix-kamailio-utils.patch refreshed. Alpine pushed a fix upstream
  that fixes the quoting issue, so this part could be dropped. I found
  some other issue with kamctl, where the prompt (for password) wasn't
  shown because OpenWrt doesn't have /dev/stderr. So I fixed that and
  added it to this patch as well. Sent upstream.
- hiredis handling was changed upstream. They changed the default
  include from "hiredis/hiredis.h" (which worked for us) to "hiredis.h".
  And the only way to get "hiredis/hiredis.h" is via pkg-config, which
  upstream doesn't allow during cross-compile, probably because hiredis
  pkg-config is rubbish. Patch added to forces pkg-config detection.
  Also includes a fix for a logical error in the Makefile regarding
  header setup. Sent upstream.
  Patch to fix hiredis pkg-config file sent upstream (also to OpenWrt
  package maintainer). Even without hiredis patch we can get away with
  forcing pkg-config detection of hiredis.
- dropped two patches that were upstreamed

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