face: use /run/nfd.sock on Linux

refs #5039

Change-Id: I10902725912a8f194ce6da6590378c1029955f80
diff --git a/systemd/nfd.service.in b/systemd/nfd.service.in
index 59058b8..ca26ec4 100644
--- a/systemd/nfd.service.in
+++ b/systemd/nfd.service.in
@@ -50,7 +50,7 @@
 # effective setting of ProtectSystem=strict
 ProtectSystem=full
 ProtectSystem=strict
-ReadWritePaths=/var/run
+ReadWritePaths=/run
 RestrictAddressFamilies=AF_UNIX AF_NETLINK AF_INET AF_INET6 AF_PACKET
 RestrictNamespaces=yes
 RestrictRealtime=yes