udevd: avoid overhead of calling rmdir on non-empty directories

udevd: avoid overhead of calling rmdir on non-empty directories

Unfortunately the linux rmdir implementation unhashes the dentry
even when the directory is not removed.  This is apparently by
design (for filesystems that don't allow deleting open files).

Results from time(1) and oprofile follow.

Before:

0.35user 0.90system
samples  %        image name               symbol name
608       9.6738  vmlinux                  shrink_dcache_parent
293       4.6619  vmlinux                  copy_page_c
271       4.3119  vmlinux                  copy_page_range
257       4.0891  udevd                    udev_rules_iter_next

After:

0.31user 0.67system
samples  %        image name               symbol name
361       5.0419  vmlinux                  copy_page_range
322       4.4972  udevd                    udev_rules_iter_next
300       4.1899  vmlinux                  copy_page_c

Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>