fix docs

lib/SNMP/Info/Layer2/Aerohive.pm

@@ -95,7 +95,8 @@ sub os {
 sub serial {
     my $aerohive = shift;
 
-    return $aerohive->ahSystemSerial();
+    return $aerohive->ahSystemSerial()
+      || $aerohive->SUPER::serial();
 }
 
 sub os_ver {
@@ -375,6 +376,10 @@ Returns the serial number extracted from C<ahSystemSerial>.
 
 =over
 
+=item $aerohive->serial()
+
+Returns C<ahSystemSerial>.
+
 =item $aerohive->layers()
 
 Returns 00000111. Layer 2 and Layer 3 functionality through proprietary MIBs.