RSSI reported by the RX descriptor requires little manipulation.
Manipulate and report the correct RSSI to the stack. This will
fix the improper signal levels reported by iwconfig iw dev wlanX
station dump. Also the Link Quality reported seems to be varying
(falls to zero also sometimes) when iperf is run from STA to AP.

Also use the default noise floor for now as the one reported
during the caliberation seems to be wrong.

The Signal and Link Quality before this patch (taken while TX is
in progress from STA to AP)

09:59:13.285428037 Link Quality=29/70  Signal level=-81 dBm
09:59:13.410660084 Link Quality=20/70  Signal level=-90 dBm
09:59:13.586864392 Link Quality=21/70  Signal level=-89 dBm
09:59:13.710296281 Link Quality=21/70  Signal level=-89 dBm
09:59:13.821683064 Link Quality=25/70  Signal level=-85 dBm
09:59:13.933402989 Link Quality=24/70  Signal level=-86 dBm
09:59:14.045839276 Link Quality=26/70  Signal level=-84 dBm
09:59:14.193926673 Link Quality=23/70  Signal level=-87 dBm
09:59:14.306230262 Link Quality=31/70  Signal level=-79 dBm
09:59:14.419459667 Link Quality=26/70  Signal level=-84 dBm
09:59:14.530711167 Link Quality=37/70  Signal level=-73 dBm
09:59:14.642593962 Link Quality=29/70  Signal level=-81 dBm
09:59:14.754361169 Link Quality=21/70  Signal level=-89 dBm
09:59:14.866217355 Link Quality=21/70  Signal level=-89 dBm
09:59:14.976963623 Link Quality=28/70  Signal level=-82 dBm
09:59:15.089149809 Link Quality=26/70  Signal level=-84 dBm
09:59:15.205039887 Link Quality=27/70  Signal level=-83 dBm
09:59:15.316368003 Link Quality=23/70  Signal level=-87 dBm
09:59:15.427684036 Link Quality=36/70  Signal level=-74 dBm
09:59:15.539756380 Link Quality=21/70  Signal level=-89 dBm
09:59:15.650549093 Link Quality=22/70  Signal level=-88 dBm
09:59:15.761171672 Link Quality=32/70  Signal level=-78 dBm
09:59:15.872793750 Link Quality=23/70  Signal level=-87 dBm
09:59:15.984421694 Link Quality=22/70  Signal level=-88 dBm
09:59:16.097315093 Link Quality=21/70  Signal level=-89 dBm

The link quality and signal level after this patch (take while
TX is in progress from STA to AP)

17:21:25.627848091 Link Quality=65/70  Signal level=-45 dBm
17:21:25.762805607 Link Quality=65/70  Signal level=-45 dBm
17:21:25.875521888 Link Quality=66/70  Signal level=-44 dBm
17:21:25.987468448 Link Quality=66/70  Signal level=-44 dBm
17:21:26.100628151 Link Quality=66/70  Signal level=-44 dBm
17:21:26.213129671 Link Quality=66/70  Signal level=-44 dBm
17:21:26.324923070 Link Quality=65/70  Signal level=-45 dBm
17:21:26.436831357 Link Quality=65/70  Signal level=-45 dBm
17:21:26.610356973 Link Quality=65/70  Signal level=-45 dBm
17:21:26.723340047 Link Quality=65/70  Signal level=-45 dBm
17:21:26.835715293 Link Quality=64/70  Signal level=-46 dBm
17:21:26.949542748 Link Quality=64/70  Signal level=-46 dBm
17:21:27.062261613 Link Quality=65/70  Signal level=-45 dBm
17:21:27.174511563 Link Quality=64/70  Signal level=-46 dBm
17:21:27.287616232 Link Quality=64/70  Signal level=-46 dBm
17:21:27.400598119 Link Quality=64/70  Signal level=-46 dBm
17:21:27.511381404 Link Quality=64/70  Signal level=-46 dBm
17:21:27.624530421 Link Quality=65/70  Signal level=-45 dBm
17:21:27.737807109 Link Quality=64/70  Signal level=-46 dBm
17:21:27.850861352 Link Quality=65/70  Signal level=-45 dBm
17:21:27.963369436 Link Quality=64/70  Signal level=-46 dBm
17:21:28.076582289 Link Quality=64/70  Signal level=-46 dBm

Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>