rc: explicitly use `-p' , it should be set but can't go wrong here

PR: https://github.com/opnsense/core/issues/1077

src/etc/rc.backup_dhcpleases

@@ -5,7 +5,7 @@ BACKUPDIR="/var/dhcpd/var/db"
 
 if [ "${1}" = "restore" ]; then
 	if [ -f "${BACKUPFILE}" ]; then
-		tar -C / -xzf "${BACKUPFILE}"
+		tar -C / -xzpf "${BACKUPFILE}"
 	fi
 else
 	if [ -d "${BACKUPDIR}" ]; then

src/etc/rc.backup_netflow

@@ -5,7 +5,7 @@ BACKUPDIR="/var/netflow"
 
 if [ "${1}" = "restore" ]; then
 	if [ -f "${BACKUPFILE}" ]; then
-		tar -C / -xzf "${BACKUPFILE}"
+		tar -C / -xzpf "${BACKUPFILE}"
 	fi
 else
 	if [ -d "${BACKUPDIR}" ]; then

src/etc/rc.backup_rrd

@@ -5,7 +5,7 @@ BACKUPFILE="/conf/rrd.tgz"
 
 if [ "${1}" = "restore" ]; then
 	if [ -f "${BACKUPFILE}" ]; then
-		tar -C / -xzf "${BACKUPFILE}"
+		tar -C / -xzpf "${BACKUPFILE}"
 	fi
 else
 	if [ -d "${BACKUPDIR}" ]; then