ext4: enable the lazy init thread when remounting read/write

ext4: enable the lazy init thread when remounting read/write

In commit a44be64bbecb ("ext4: don't clear SB_RDONLY when remounting
r/w until quota is re-enabled") we defer clearing tyhe SB_RDONLY flag
in struct super.  However, we didn't defer when we checked sb_rdonly()
to determine the lazy itable init thread should be enabled, with the
next result that the lazy inode table initialization would not be
properly started.  This can cause generic/231 to fail in ext4's
nojournal mode.

Fix this by moving when we decide to start or stop the lazy itable
init thread to after we clear the SB_RDONLY flag when we are
remounting the file system read/write.

Fixes a44be64bbecb ("ext4: don't clear SB_RDONLY when remounting r/w until...")

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20230527035729.1001605-1-tytso@mit.edu
Signed-off-by: Theodore Ts'o <tytso@mit.edu>