flowtop: Constify function parameter in walk_process()

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
geoip: Pass struct sockaddr_in{,6} as pointer instead of by value

Change the interface to the geoip_* functions to take a pointer to a
struct sockaddr_in{,6} instead of the struct itself.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
build: Remove unused CONFIG_LIBGEOIP

If libgeoip is present, CONFIG_GEOIP will be set later on depending on
HAVE_LIBGEOIP, we thus don't need to write CONFIG_LIBGEOIP to Config.
This symbol isn't used anywhere in the build process.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
build: Allow to build astraceroute and flowtop without GeoIP support

Both tools are already prepared to handle NULL return values of the
geoip_* lookup functions, so we might as well build them without geoip
support if not needed/present.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>