package/avahi: does not build with static-only

... and propagate to reverse dependencies.

Fixes (which I reproduced here):
    http://autobuild.buildroot.net/results/ea2/ea2c8f20c4032bf82876805ea787a55834091cec

Should fix (which I did not even try to reproduce):
    http://autobuild.buildroot.net/results/4ef/4ef5bfc17f50bddb00f7ef3d62fc1fe963b7da82
    http://autobuild.buildroot.net/results/76e/76e4854812b0ef3862c080eead4012b35ef27f0f
    http://autobuild.buildroot.net/results/5bf/5bfb3fd9fe61bef5f998dc5999ce2060c334662c
    http://autobuild.buildroot.net/results/dc6/dc607c35471ef6dda04e06ad05ae7794615af578



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <jacmet@uclibc.org>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>