Add hostapd options wpa_group_update_count and wpa_pairwise_update_count

Add hostapd options wpa_group_update_count and wpa_pairwise_update_count

wpa_group_update_count and wpa_pairwise_update_count can now be used to
set the GTK and PTK rekey retry limits (dot11RSNAConfigGroupUpdateCount
and dot11RSNAConfigPairwiseUpdateCount). Defaults set to current
hardcoded value (4).

Some stations may suffer from frequent deauthentications due to GTK
rekey failures: EAPOL 1/2 frame is not answered during the total timeout
period of currently ~3.5 seconds. For example, a Galaxy S6 with Android
6.0.1 appears to go into power save mode for up to 5 seconds. Increasing
wpa_group_update_count to 6 fixed this issue.

Signed-off-by: Günther Kelleter <guenther.kelleter@devolo.de>