configure, netsniff-ng: make netsniff-ng's geoip dependency optional

Geoip dependency should not be mandatory as it's not a core part of
netsniff-ng. This also facilitates compilation on platforms where
geoip is not available.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
netsniff-ng: fix recognition of -U command line option

"-U" has been forgotten to add into shortopts. "--update" works as
expeceted however. So simply add "U".

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