[config] Enable WPA2 by default

Wireless gPXE images are already so large that user-friendliness
seems to trump ROM-size friendliness in this case.

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/config/general.h

  */
 #define	CRYPTO_80211_WEP	/* WEP encryption (deprecated and insecure!) */
 #define	CRYPTO_80211_WPA	/* WPA Personal, authenticating with passphrase */
-#undef	CRYPTO_80211_WPA2	/* Add support for stronger WPA cryptography */
+#define	CRYPTO_80211_WPA2	/* Add support for stronger WPA cryptography */
 
 /*
  * Name resolution modules