diag_arp.php: Teach the ARP Table display to also display the status
The status of ARP entries is important, but the status is not shown in the GUI. Additionally, incomplete ARP entries are not shown and they would also be useful to see.
Improve the ARP table display. Implements #6822
Shows incomplete ARP entries, which were skipped before (for no reason I could find in the commit history)
Shows a status column indicating if an entry is permanent (static), expired, or when it will expire
Shows a Link Type column that indicates if an entry is using Ethernet, VLAN, etc.