apparmor: use @{PROC} instead of /proc, allow read on sys.net.ipv4.ip_local_port_range.
apparmor: use @{PROC} instead of /proc, allow read on sys.net.ipv4.ip_local_port_range.

Addresses-Ubuntu-Bug: 1552441

tjaalton/bind9,tjaalton/bind9,tjaalton/bind9,tjaalton/bind9,tjaalton/bind9,tjaalton/bind9