lldpd: fix autoreconf failure

lldpd: fix autoreconf failure

The lldpd sources ship a modified local AX_LIB_READLINE M4 macro which
conflicts with the official macro shipped by autoconf-archive.

Due to the official macro having the same name and a higher serial
number, autoconf will prefer including that one instead of the local
copy, preventing the substitution of @READLINE_LIBS@ in Makefile.in
templates, ultimately leading to the following build failure when
linking lldpcli:

    ...-gcc: error: READLINE_LIBS@: No such file or directory

Avoid this problem by renaming the locally shipped macro to not clash
with the official implementation anymore.

Ref: https://github.com/lldpd/lldpd/pull/423
Acked-by: Stijn Tintel <stijn@linux-ipv6.be>
Tested-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>