contrib/unbound{,_portable}.service.in:
With the changes introduced in f6a527c25a
it is now necessary to also allow access to the AF_NETLINK socket
address family to be able to get information from interfaces.
Without the AF_NETLINK address family the systemd service errors with:
```
error: failed to list interfaces: getifaddrs: Address family not
supported by protocol
```
Fixes#350
Pidfiles aren't needed while running unbound through systemd.
The PID of the unbound daemon can still be obtained with:
'systemctl show --property MainPID --value unbound'.
While disabling pidfiles we can also drop CAP_CHOWN and writable
/run directory.
CAP_IPC_LOCK controls whether a process can lock pages into physical
memory (for instance to prevent passwords or private keys from
being swapped to disk), e.g. mmap() with the MAP_LOCKED flag or
shmctl() with the SHM_LOCK command, neither of which seem to be
used by unbound.
State directory will be created under /var/lib/unbound and will be
useful for writing various files managed at runtime like trust
anchors updates there instead of in ConfigureDirectory which could
be made read-only next. For this chroot needs to be disabled.
The real purpose of this service is to make it work with
https://systemd.io/PORTABLE_SERVICES/ which are incompatible with
chroot workarounds from original unbound.service.
The service content is identical to unbound.service with exception
for chroot related rules which were modified as needed.
