config: check for libz

Add a configure extension to check for libz that is needed for the
geoip updater.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
config: check for liburcu

Add a configure script extension that checks for liburcu as it is
currently needed by flowtop.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>