copy: change the various copy_xyz() calls to take a unified flags parameter

This adds a unified "copy_flags" parameter to all copy_xyz() function
calls, replacing the various boolean flags so far used. This should make
many invocations more readable as it is clear what behaviour is
precisely requested. This also prepares ground for adding support for
more modes later on.

src/nspawn/nspawn.c

@@ -1364,7 +1364,7 @@ static int setup_resolv_conf(const char *dest) {
         }
 
         /* If that didn't work, let's copy the file */
-        r = copy_file("/etc/resolv.conf", where, O_TRUNC|O_NOFOLLOW, 0644, 0);
+        r = copy_file("/etc/resolv.conf", where, O_TRUNC|O_NOFOLLOW, 0644, 0, COPY_REFLINK);
         if (r < 0) {
                 /* If the file already exists as symlink, let's suppress the warning, under the assumption that
                  * resolved or something similar runs inside and the symlink points there.
@@ -3700,7 +3700,7 @@ int main(int argc, char *argv[]) {
                                 goto finish;
                         }
 
-                        r = copy_file(arg_image, np, O_EXCL, arg_read_only ? 0400 : 0600, FS_NOCOW_FL);
+                        r = copy_file(arg_image, np, O_EXCL, arg_read_only ? 0400 : 0600, FS_NOCOW_FL, COPY_REFLINK);
                         if (r < 0) {
                                 r = log_error_errno(r, "Failed to copy image file: %m");
                                 goto finish;
@@ -3856,7 +3856,7 @@ finish:
 
         /* Try to flush whatever is still queued in the pty */
         if (master >= 0) {
-                (void) copy_bytes(master, STDOUT_FILENO, (uint64_t) -1, false);
+                (void) copy_bytes(master, STDOUT_FILENO, (uint64_t) -1, 0);
                 master = safe_close(master);
         }