hostapd: fix missing HS20 support for hostapd-full

commit c3a4cdd ("hostapd: remove hostapd-hs20 variant")
as well as
commit 9f19271 ("hostapd: wpas: add missing config symbols")
indicate hostapd-full should support Hotspot 2.0 already, but only
wpa_supplicant (and wpad) do.

How this happened is not really clear, as no commit adding support for
Hotspot 2.0 is in the history.

Fix this and add Hotspot 2.0 capability to hostapd-full.

Signed-off-by: David Bauer <mail@david-bauer.net>

package/network/services/hostapd/files/hostapd-full.config

@@ -316,7 +316,7 @@ CONFIG_INTERNAL_LIBTOMMATH=y
 CONFIG_INTERWORKING=y
 
 # Hotspot 2.0
-#CONFIG_HS20=y
+CONFIG_HS20=y
 
 # Enable SQLite database support in hlr_auc_gw, EAP-SIM DB, and eap_user_file
 #CONFIG_SQLITE=y