Transceiver52M: add antenna selection from configuration

Set optional transmit and receive antennas from database configuration
file. Use default antenna values on empty string or if option does not
exist.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
transceiver: workaround for transmit testing with no clock reset

Non-functional clock reset causes huge initial timing offset
between expected and received timestamps. Receive an initial
packet to 'set' the expected starting timestamp value for
both transmit and receive.

Signed-off-by: Thomas Tsou <ttsou@vt.edu>
umtrx: flush any possible garbage bursts at start

In certain cases (higher sample-per-symbol counts), there is
some sensitivity to either timeouts or bad metadata on the
first packet. The first packet sets the transceiver clock, so
this is essential. As a workaround, drop the first 50 packets
to guarantee that we get a packet with a valid timestamp

Signed-off-by: Thomas Tsou <ttsou@vt.edu>
Modified fillerTable usage in pushRadioVector function.

Now we put to fillerTable only frames of BEACON channels, all others frames in fillerTable are dummy bursts.
Transceiver52M: Check for correctly set TSC before setting timeslot types.
Transceier52M: Make error response to an unknown command on UDP command interface more understandable.

Previously we just repeated the last response which could confuse a command sender.
Handover support for transceiver (TCH/F TCH/H SDCCH4 SDCCH8)

It allows to enable/disable access burst detection on each subslot
individually. It should be compatible with the handover implementation
at OsmoBTS and OpenBTS.

Original authors: Dmitry Soloviev <Dmitri.Soloviev@fairwaves.ru>, Andreas Eversberg <andreas@eversberg.eu>
Transceiver52M: hack for transmitter disable with power off command

This patch will simply disable the tx burst submission at the output of
the filler table when the POWEROFF command is issued.

A more complicated patch would involve thread control or resource deallocation.
Basically, we can do something cheap and simple like this patch, or something
that deals with the existing shutdown/resource management issues. The latter
requires much more effort and thus we pospone it.
umtrx: set timing offset and clocking frequency

Measured offset and set to zero based on Nokia 3120 handset.

Signed-off-by: Thomas Tsou <tom@tsou.cc>