Get rx link speed through signalPoll cmd

Get the last received packet bit rate in Mbps
through signalPoll() call and save it in WifiInfo.

Bug: 118820339
Test: Manual test by connecting to AP
Test: ./tests/wifitests/runtests.sh
Change-Id: I883b6e9e650843dd76beff835cfcf1b10a6aeeb3
5 files changed