package/wireless-regdb: bump version to 2021.08.28

Changelog (since 2021.04.21):

  47007d0 wireless-regdb: update regulatory database based on preceding changes
  e983a25 Update regulatory rules for Ecuador (EC)
  a0bcb88 wireless-regdb: Update regulatory rules for Norway (NO) on 6 and 60 GHz
  cdf854d wireless-regdb: Update regulatory rules for Germany (DE) on 6GHz
  a4468e8 wireless-regdb: update regulatory database based on preceding changes
  86cba52 wireless-regdb: reduce bandwidth for 5730-5850 and 5850-5895 MHz in US
  6fa2384 wireless-regdb: remove PTMP-ONLY from 5850-5895 MHz for US
  9839e1e wireless-regdb: recent FCC report and order allows 5850-5895 immediately
  42dfaf4 wireless-regdb: update 5725-5850 MHz rule for GB

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>