N310: incorrect behaviour if BW is set starting with UHD version 4.2.0

[thomas-schlichter]

Issue Description

If the RX BW is changed via uhd::usrp::multi_usrp::set_rx_bandwidth(), the N310 daughterboard is re-initialized and seems to lose some of its configuration, what leads to not correctly receiving the expected signal.

Setup Details

N310 with UHD library version 4.3.0.

I provided a CW at 2169.08 MHz and wanted to observe it using the rx_ascii_art_dft example tool provided with the UHD library.
The working command:

/usr/lib/uhd/examples/rx_ascii_art_dft --args "type=n3xx,clock_source=internal,master_clock_rate=122880000" --rate 61440000 --freq 2169080000 --gain 50

The non-working command:

/usr/lib/uhd/examples/rx_ascii_art_dft --args "type=n3xx,clock_source=internal,master_clock_rate=122880000" --rate 61440000 --freq 2169080000 --gain 50 --bw 40000000

Expected Behavior

Also when setting the RX BW to 40 MHz instead of the default 100 MHz, the CW should be correctly received.

Actual Behaviour

Only when not changing the RX BW, the CW is correctly received.

Steps to reproduce the problem

See above.

Additional Information

I think the issue was introduced with commit a8ad491.
Before, changing the RX BW was basically a NOP.