package/netsniff: fix missing depend on statements

Add missing architecture dependencies inherited from liburcu.

Fixes:
  http://autobuild.buildroot.org/results/0a9/0a90d7c8f523b90b8a4ca6312ab4835547590fb2/



Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>