cfg80211: fix BSS comparison

Since the BSS table is organized in a RB tree, the BSSs need to be
comparable. This means that we must define a < and > operator to
the BSS object.
compare_ethr_addr isn't enough since it returns only a binary value.

Since Felix's

cfg80211: use compare_ether_addr on MAC addresses instead of memcmp

    Because of the constant size and guaranteed 16 bit alignment, the inline
    compare_ether_addr function is much cheaper than calling memcmp.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

The BSS table is corrupted: rb_find_bss can't find the bss.
As a result BSSes are duplicated in the BSS table, and we get stuck
while probing an AP before associating (in STA mode).

Change-Id: I85928756f4328028230832c1565ece7f412f3843
CC: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/scan.c

@@ -378,7 +378,11 @@ static int cmp_bss_core(struct cfg80211_bss *a,
 			       b->len_information_elements);
 	}
 
-	return compare_ether_addr(a->bssid, b->bssid);
+	/*
+	 * we can't use compare_ether_addr here since we need a < > operator.
+	 * The binary return value of compare_ether_addr isn't enough
+	 */
+	return memcmp(a->bssid, b->bssid, sizeof(a->bssid));
 }
 
 static int cmp_bss(struct cfg80211_bss *a,