Allow configuring arbitrary gain settings

[devicenull]

This adds a "gain_settings" option to sources, which allows you to configure arbitrary gain stages by name. For example, to fix some of the RSP1A issues from #422:

"gain_settings": {
  "RFGR": 1,
  "IFGR": 25
 }

I am not a C developer, so uh.. you get to keep both pieces if this breaks. I did not remove any of the existing gain config settings - these will override anything set in this new array.

[robotastic]

This looks pretty good! The only thing I can think that is missing is that the gain values are not really saved anywhere in the source. I might add a little code that creates a vector of the gain values. This could be useful for sending the config of the Source off to somewhere else.

[devicenull]

Great! It looks like this will also resolve #489 and possibly #290

[robotastic]

Ok - I have gone a bit off the deep end and I am reworking the whole gain section to be based on around this... Mostly just changes under the hood.

[devicenull]

That looks pretty good to me! I guess at some point you'll want to remove the non-array config options there, but no real reason to break backwards compatibility now.

[robotastic]

Agreed - I am just keeping the old way around for compatibility, but it could all be moved to the settings array. Thanks for putting this together!!

[gisforgirard]

just wanted to say, I tested it and appears to have fixed issues I was having with a bladeRF x40 where gains weren't being set properly, they appear to set perfectly fine now... the bladeRF 2.0 xA9 on the other hand, I think might be totally useless in its ability to set gains but that's their fault, not yours...

before:

[WARNING @ host/libraries/libbladeRF/src/board/bladerf1/bladerf1.c:1825] bladerf1_set_gain_stage: gain stage 'LNA' invalid
[WARNING @ host/libraries/libbladeRF/src/board/bladerf1/bladerf1.c:1869] bladerf1_get_gain_stage: gain stage 'LNA' invalid
[WARNING @ host/libraries/libbladeRF/src/board/bladerf1/bladerf1.c:1869] bladerf1_get_gain_stage: gain stage 'LNA' invalid
[2021-11-12 02:31:22.313465] (info) LNA Gain set to: 0

after (using gainSettings and lowercase "lna" plus the other two differently named gain settings):

FOUND lna
FOUND rxvga1
FOUND rxvga2
[2021-11-12 02:32:46.052332] (info) Gain Stage: system supported values: -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
[2021-11-12 02:32:46.052344] (info) Gain Stage: lna supported values: 0 3 6
[2021-11-12 02:32:46.052358] (info) Gain Stage: rxvga1 supported values: 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
[2021-11-12 02:32:46.052366] (info) Gain Stage: rxvga2 supported values: 0 3 6 9 12 15 18 21 24 27 30
[2021-11-12 02:32:46.052821] (info) lna Gain set to: 3
[2021-11-12 02:32:46.053272] (info) rxvga1 Gain set to: 18
[2021-11-12 02:32:46.053705] (info) rxvga2 Gain set to: 21

no errors at all! nice!