Fully empty feedline config throws weird error

[JennySmith888]

fc = FeedlineConfig(bitstream=BitstreamConfig(), rfdc_clk=RFDCClockingConfig(), rfdc=RFDCConfig(), if_board=IFConfig(), waveform=WaveformConfig(), chan=ChannelConfig(), ddc=DDCConfig(), filter=FilterConfig(), trig=TriggerConfig())

Will throw an event loop error RuntimeError: There is no current event loop in thread "TapThread: adc:b'1540791414205196776'".

if it's the first capture request and there's no bitstream downloaded. It will likely work if a previous capture request has been sent with BitstreamConfig(), RFDCCockingConfig(), and RFDCConfig() defined. This is weird behavior and it would be nice to throw a better error here.

[JennySmith888]

Jeb suggests a helper code along the lines
def FCFactory(**default_confgs): return fuctools.partial(FeedlineConfig, kwargs=default_confgs)
fac = FCFactory(bitstream=mybsconfig, clocking=myclocking, rfdc=myrfdc)

[JennySmith888]

May want to make empty BitstreamConfig(), RFDCClockingConfig(), and RFDCConfig() illegal in some cases...