package/quagga: unconditionally create /etc/quagga

package/quagga: unconditionally create /etc/quagga

/etc/quagga is listed in QUAGGA_PERMISSIONS, but is only created when
some of the quagga sub-options are enabled. When none of those
sub-options are enabled, /etc/quagga is not created, causing a build
failure when the filesystem images are created:

makedevs: line 1: recursive failed for /home/thomas/projets/outputs/quagga-minimal/build/buildroot-fs/tar/target/etc/quagga: No such file or directory

Since it is too cumbersome to maintain which sub-options exactly lead
to /etc/quagga being created, simply create /etc/quagga
unconditionally. It will simply be empty when the quagga package
doesn't install anything in it.

For the record, here is the list of files installed in /etc/quagga
when all quagga sub-options are enabled:

  bgpd.conf.sample bgpd.conf.sample2 isisd.conf.sample
  ospf6d.conf.sample ospfd.conf.sample pimd.conf.sample
  ripd.conf.sample ripngd.conf.sample vtysh.conf.sample
  zebra.conf.sample

Fixes:

  http://autobuild.buildroot.net/results/cdb66589909fd3996186f7db7d1f19a3b03d58a0/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>