shill: Adds BSS nl80211 attribute.

The BSS attribute, which is contained in the
NL80211_CMD_NEW_SCAN_RESULTS netlink message, contains SSID information
received from a scan.

BUG=chromium:221118
TEST=unittest.

Change-Id: I20766ae6d73ae5729e4ae8de47cac8bcbf5b3fe9
Reviewed-on: https://gerrit.chromium.org/gerrit/48013
Reviewed-by: Wade Guthrie <wdg@chromium.org>
Tested-by: Wade Guthrie <wdg@chromium.org>
Commit-Queue: Wade Guthrie <wdg@chromium.org>
diff --git a/attribute_list.h b/attribute_list.h
index 1e6503d..58ad37b 100644
--- a/attribute_list.h
+++ b/attribute_list.h
@@ -49,6 +49,9 @@
   // attributes exist).
   ByteString Encode() const;
 
+  // Create, get, and set attributes of the given types.  Attributes are
+  // accessed via an integer |id|.  |id_string| is a string used to describe
+  // the attribute in debug output.
   bool CreateU8Attribute(int id, const char *id_string);
   bool SetU8AttributeValue(int id, uint8_t value);
   bool GetU8AttributeValue(int id, uint8_t *value) const;
@@ -74,6 +77,8 @@
   bool IsFlagAttributeTrue(int id) const;
 
   bool CreateStringAttribute(int id, const char *id_string);
+  // SSID attributes are derived from string attributes.
+  bool CreateSsidAttribute(int id, const char *id_string);
   bool SetStringAttributeValue(int id, std::string value);
   bool GetStringAttributeValue(int id, std::string *value) const;