BACKPORT: ext4: optimize match for casefolded encrypted dirs

[ Upstream commit 1ae98e295fa2577fb5e492200c58d10230e00e99 ]

Matching names with casefolded encrypting directories requires
decrypting entries to confirm case since we are case preserving. We can
avoid needing to decrypt if our hash values don't match.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Link: https://lore.kernel.org/r/20210319073414.1381041-3-drosen@google.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Change-Id: Ic74307e53dc59ec47575f33c56e291ccd137520d