User with only "WebCfg - Firewall: NAT: Port Forward" cannot view the list of port forwards
A user with the "WebCfg - Firewall: NAT: Port Forward" privilege can open firewall_nat.php but none of the port forward entries are displayed in the list.
If the user also has "WebCfg - Firewall: NAT: Port Forward: Edit" then the entries are show.
1:1 NAT and Outbound NAT pages appear to be OK, only port forwards suffer from this issue.
Be specific with port fwd priv checks. Fixes #8563
This way, users with only privs to view but not edit port forwards can still see the entries, but not act upon them.