Make check_20mhz_bss() static

This is not used outside this file anymore, so there is no need to
export the symbol either.

Signed-off-by: Jouni Malinen <j@w1.fi>

src/common/hw_features_common.c

@@ -237,7 +237,8 @@ int check_40mhz_5g(struct hostapd_hw_modes *mode,
 }
 
 
-int check_20mhz_bss(struct wpa_scan_res *bss, int pri_freq, int start, int end)
+static int check_20mhz_bss(struct wpa_scan_res *bss, int pri_freq, int start,
+			   int end)
 {
 	struct ieee802_11_elems elems;
 	struct ieee80211_ht_operation *oper;

src/common/hw_features_common.h

@@ -26,7 +26,6 @@ void get_pri_sec_chan(struct wpa_scan_res *bss, int *pri_chan, int *sec_chan);
 int check_40mhz_5g(struct hostapd_hw_modes *mode,
 		   struct wpa_scan_results *scan_res, int pri_chan,
 		   int sec_chan);
-int check_20mhz_bss(struct wpa_scan_res *bss, int pri_freq, int start, int end);
 int check_40mhz_2g4(struct hostapd_hw_modes *mode,
 		    struct wpa_scan_results *scan_res, int pri_chan,
 		    int sec_chan);