radio: silabs: Fix the issue with AF jump

- Initiate AF jump when AF list has minimum 1 entry.
- Wait for certain time and calculate the avg RSSI value and
  initiate AF if avg rssi is less than threshold value.
- Keep the original AF list if AF jump not happened.
- Process RT+ & eRT only when valid data available.

CRs-Fixed: 732776
Change-Id: I8bdbab6953c6b6c019f87935e8402a3b1ae9f7af
Signed-off-by: Venkateshwarlu Domakonda <vdomak@codeaurora.org>