utils: usrp_n2xx_net_burner_gui no longer ignores dont-check-rev option
uhd: fix get_xx_freq_range to use analog bw/2

The proper equation should be:

max_freq = max_lo + min(adc/2, bw/2) - sr/2
usrp2: fix firmware rx clear register offset

When an ICMP dest unreachable pkt arrives,
the fw needs to know how to shutoff the DSP.
This offset for the reset register was
broken by a previous fix for register overlap.