systemctl/core: ignore masked units in preset-all

With any masked unit that would that would be enabled by presets, we'd get:

test@rawhide $ sudo systemctl preset-all
Failed to execute operation: Unit file is masked.

test@rawhide $ sudo systemctl --root=/ preset-all
Operation failed: Cannot send after transport endpoint shutdown

Simply ignore those units:

test@rawhide $ sudo systemctl preset-all
Unit xxx.service is masked, ignoring.

1 files changed, 5 insertions, 0 deletions

diff --git a/src/shared/install.h b/src/shared/install.h
index 6f8b45d4f6..6b760def9b 100644
--- a/src/shared/install.h
+++ b/src/shared/install.h
@@ -72,10 +72,15 @@ enum UnitFilePresetMode {
 enum UnitFileChangeType {
         UNIT_FILE_SYMLINK,
         UNIT_FILE_UNLINK,
+        UNIT_FILE_IS_MASKED,
         _UNIT_FILE_CHANGE_TYPE_MAX,
         _UNIT_FILE_CHANGE_TYPE_INVALID = -1
 };
 
+static inline bool unit_file_change_is_modification(UnitFileChangeType type) {
+        return IN_SET(type, UNIT_FILE_SYMLINK, UNIT_FILE_UNLINK);
+}
+
 struct UnitFileChange {
         UnitFileChangeType type;
         char *path;