package/minidlna: unavailable for static builds

package/minidlna: unavailable for static builds

minidlna has long standing issues with static-only builds:
http://patchwork.ozlabs.org/patch/501844/
http://patchwork.ozlabs.org/patch/506310/

This patch fixes
http://autobuild.buildroot.net/results/d73/d7370d0f8d1c7c028996feab0ea4f36edbf8a698/
http://autobuild.buildroot.net/results/575/5752be7c1820579425ba24178482ab0d6eea7b62/
"pack_utils.c:(.text+0x9a8): multiple definition of `free_metadata'"

The multiple definition can be fixed of course but instead of digging
deeper and deeper into this mess let's disable static builds.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>