driver_bsd: Fix build without SIOCS80211CHANNEL

At least FreeBSD 7 does not seem to define this and failed to build
after the previous changes.

src/drivers/driver_bsd.c

@@ -488,6 +488,7 @@ bsd_send_eapol(struct l2_packet_data *sock_xmit, const u8 *addr,
 static int
 bsd_set_freq(int s, const char *ifname, u16 channel)
 {
+#ifdef SIOCS80211CHANNEL
 	struct ieee80211chanreq creq;
 	u32 mode;
 
@@ -507,6 +508,11 @@ bsd_set_freq(int s, const char *ifname, u16 channel)
 	os_strlcpy(creq.i_name, ifname, sizeof(creq.i_name));
 	creq.i_channel = channel;
 	return ioctl(s, SIOCS80211CHANNEL, &creq);
+#else
+	wpa_printf(MSG_ERROR, "bsd_set_freq: SIOCS80211CHANNEL not "
+		   "defined");
+	return -1;
+#endif
 }