update: correctly strip the locks on major upgrade

We don't want them to linger after having performed the major
upgrade.  This is consistent with package behaviour.

update/opnsense-update.sh

@@ -567,15 +567,15 @@ if [ "${DO_PKGS}" = "-p" ]; then
 fi
 
 if [ "${DO_BASE}" = "-b" ]; then
-	if [ -z "${DO_FORCE}" ]; then
+	if [ -z "${DO_FORCE}" -o -n "${DO_UPGRADE}" ]; then
 		rm -f ${VERSIONDIR}/base.lock
 	fi
 	fetch_set ${OBSOLETESET}
 	fetch_set ${BASESET}
 fi
 
 if [ "${DO_KERNEL}" = "-k" ]; then
-	if [ -z "${DO_FORCE}" ]; then
+	if [ -z "${DO_FORCE}" -o -n "${DO_UPGRADE}" ]; then
 		rm -f ${VERSIONDIR}/kernel.lock
 	fi
 	fetch_set ${KERNELSET}