[4481] Add missing description of query6 argument to lease6_select

src/bin/dhcp6/dhcp6_hooks.dox

@@ -111,6 +111,7 @@ packet processing. Hook points that are not specific to packet processing
 @subsection dhcpv6HooksLease6Select lease6_select
 
  - @b Arguments:
+   - name: @b query6, type: isc::dhcp::Pkt6Ptr, direction: <b>in/out</b>
    - name: @b subnet6, type: isc::dhcp::Subnet6Ptr, direction: <b>in</b>
    - name: @b fake_allocation, type: bool, direction: <b>in</b>
    - name: @b lease6, type: isc::dhcp::Lease6Ptr, direction: <b>in/out</b>