[802.11] Use correct name for sec80211_detect()

The workhorse function for detecting 802.11 security was still named
_sec80211_detect(), a holdover from the old style of weak function
handling, with the result that all networks would be identified as
"unknown".

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/80211/sec80211.c

  * it. If it does not exist, any network with the PRIVACY bit set in
  * beacon->capab should be considered unknown.
  */
-int _sec80211_detect ( struct io_buffer *iob,
-		       enum net80211_security_proto *secprot,
-		       enum net80211_crypto_alg *crypt )
+int sec80211_detect ( struct io_buffer *iob,
+		      enum net80211_security_proto *secprot,
+		      enum net80211_crypto_alg *crypt )
 {
 	struct ieee80211_frame *hdr = iob->data;
 	struct ieee80211_beacon *beacon =