package/libnss: need dynamic library support

Fixes:
  http://autobuild.buildroot.net/results/e01733c4b8c23f62e2081f0c4aadc16e22c4a2c4/



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>