[link-metrics] add missing initialization of noisefloor for link metrics

[Irving-cl]

The PR adds missing initialization of noise floor in link metrics
module. Without the PR, the link margin obtained in link metrics
enhanced-ack probing is incorrect.

On simulation platform, the initialization is done:
https://github.com/openthread/openthread/blob/main/examples/platforms/simulation/radio.c#L503

[zhanglongxia]

LGTM

[edmont]

LGTM, thanks.

However, wouldn't be less error prone if the Link Metrics module would initialize the noise floor itself? I.e., using SubMac::GetNoiseFloor.

[Irving-cl]

LGTM, thanks.

However, wouldn't be less error prone if the Link Metrics module would initialize the noise floor itself? I.e., using SubMac::GetNoiseFloor.

SG. That needs adding a new platform API and SPINEL method to set the noise floor at the RCP. I can do it later.

[edmont]

SG. That needs adding a new platform API and SPINEL method to set the noise floor at the RCP. I can do it later.

Hi @Irving-cl, any update on this?

[Irving-cl]

@edmont Sorry I'm quite busy these days. Would you like to add it if you have time?

[edmont]

@Irving-cl I'm also busy, just checking if changes were expected around this, but not hard requirement. Let's leave it for sometime later.