ext4: don't set up encryption key during jbd2 transaction

Commit a80f7fcf ("ext4: fixup ext4_fc_track_* functions' signature")
extended the scope of the transaction in ext4_unlink() too far, making
it include the call to ext4_find_entry().  However, ext4_find_entry()
can deadlock when called from within a transaction because it may need
to set up the directory's encryption key.

Fix this by restoring the transaction to its original scope.

Reported-by:  <syzbot+1a748d0007eeac3ab079@syzkaller.appspotmail.com>
Fixes: a80f7fcf ("ext4: fixup ext4_fc_track_* functions' signature")
Cc: <stable@vger.kernel.org> # v5.10+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20221106224841.279231-3-ebiggers@kernel.org


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