The value for tx power is reported incorrectly

[testuser7]

The value for tx power is reported incorrectly:

root@MX8500:/usr/bin# ubus call iwinfo txpowerlist '{"device": "phy5-ap0"}'
{
	"results": [
		{
			"dbm": 255,
			"mw": 2147483647,
			"active": false
		}
	]
}

iwinfo displays this value correctly after the last update:

root@MX8500:/usr/bin# iwinfo phy5-ap0 txpowerlist
   0 dbm (   1 mW)
   1 dbm (   1 mW)
   2 dbm (   1 mW)
   3 dbm (   1 mW)
   4 dbm (   2 mW)
   5 dbm (   3 mW)
   6 dbm (   3 mW)
   7 dbm (   5 mW)
   8 dbm (   6 mW)
   9 dbm (   7 mW)
  10 dbm (  10 mW)
  11 dbm (  12 mW)
  12 dbm (  15 mW)
  13 dbm (  19 mW)
  14 dbm (  25 mW)
  15 dbm (  31 mW)
  16 dbm (  39 mW)
  17 dbm (  50 mW)
  18 dbm (  63 mW)
  19 dbm (  79 mW)
* 20 dbm ( 100 mW)
  21 dbm ( 125 mW)
  22 dbm ( 158 mW)
  23 dbm ( 199 mW)
  24 dbm ( 251 mW)