asterisk-chan-sccp: autoconf fixes

asterisk-chan-sccp: autoconf fixes

Since OpenWrt updated autoconf to 2.71 configure fails, because
"$ac_dir" is now empty when configure attempts to run
"./tools/versioncheck". With previous autoconf "$ac_dir" contained
"autoconf" at this point in the script.

As a workaround "$ac_dir" is replaced with "$ac_aux_dir", which
incidentally contains "autoconf".

Also a build dependency is added for gettext-full, as it provides
iconv.m4. Previously this was provided by libiconv, but not anymore.
Without iconv.m4 autoreconf fails.

Some patches were refreshed to allow CI to pass.

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