buildroot

olsr: disable in musl configurations

olsr doesn't build on musl, so let's disable it. The issue has been
reported upstream at https://github.com/OLSR/olsrd/issues/6.

Fixes:

  http://autobuild.buildroot.net/results/74cff8fc87d95d70840394fc049fc038797b9888/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>