Fix the number of buckets in Net.Wifi.InterfaceCount UMA histogram.

The number of buckets should be one more than currently specified.
Otherwise the histogram buckets the values 3 and 4 in the same bucket.

BUG=

Review URL: https://codereview.chromium.org/547693002

Cr-Commit-Position: refs/heads/master@{#294808}

content/browser/geolocation/wifi_data_provider_corewlan_mac.mm

@@ -168,7 +168,7 @@ bool CoreWlanApi::GetAccessPointData(WifiData::AccessPointDataSet* data) {
       [supported_interfaces count] - interface_error_count,
       1,
       5,
-      5);
+      6);
 
   // Return true even if some interfaces failed to scan, so long as at least
   // one interface did not fail.

content/browser/geolocation/wifi_data_provider_win.cc

@@ -245,7 +245,7 @@ void WindowsWlanApi::LogWlanInterfaceCount(int count) {
       count,
       1,
       5,
-      5);
+      6);
 }
 
 bool WindowsWlanApi::GetAccessPointData(