This extends osmo_nitb to offer a UDP feed of real-time measurement
reports, which can be used by (a variety of) external tools for
visualization or other processing.
We also add a small ncurses based tool (meas_vis) which shows a
baragraph display of the last few mobile stations that were active,
indicating their uplink/downlink receive level and quality.
<WARNING>
This sends non-portable structures like gsm_meas_rep over UDP
and assumes the receiver has identical alignment and endianness! Before
this feature is merged, it either needs to be converted to a unix domain
socket (but they don't do multicast, which would be nice) or the wire
format needs to change into something portable with defined alignment
and encoding
</WARNING>
