services_dhcp.php: DHCP Static Mappings table should be sortable
Currently the `DHCP Static Mappings table` inside `Services->DHCP Server` isn't sortable where it should be.
Aside from that wouldn't it be rather nice to have all of the available tables sortable? Actually I'd bet that's what most users would expect from tables in general.
Fixed #6504 by making table sortable
(cherry picked from commit 55f67b5abd9b809807e328477779d97120908273)