loudmouth: fix autoconf errors

loudmouth: fix autoconf errors

Do not override configure recipe and do not invoke upstream autogen.sh.
The shipped autogen.sh attempts to call "gtkdocize" which is no guaranteed
build prereq of LEDE or OpenWrt.

Also add a patch to disable the processing of documentation, tests and
examples as these resources rely on gtk-doc infrastructure which is not
available within LEDE or OpenWrt.

Example error for the bad autogen.sh invocation:

    ( cd .../loudmouth-1.5.3; ./autogen.sh )
    ./autogen.sh: 33: ./autogen.sh: gtkdocize: not found
    Makefile:73: recipe for target '.../.configured_yynyyyyn' failed

Example error for the lacking gtk-doc automake infrastructure:

    automake: error: cannot open < gtk-doc.make: No such file or directory
    autoreconf: .../host/bin/automake failed with exit status: 1
    [...]
    config.status: error: cannot find input file: `docs/reference/Makefile.in'
    Makefile:72: recipe for target '.../.configured_yynyn' failed

Signed-off-by: Jo-Philipp Wich <jo@mein.io>