reiserfs: unpack tails on quota files

Quota files cannot have tails because quota_write and quota_read functions do
not support them.  So far when quota files did have tail, we just refused to
turn quotas on it.  Sadly this check has been wrong and so there are now
plenty installations where quota files don't have NOTAIL flag set and so now
after fixing the check, they suddently fail to turn quotas on.  Since it's
easy to unpack the tail from kernel, do this from reiserfs_quota_on() which
solves the problem and is generally nicer to users anyway.

Signed-off-by: Jan Kara <jack@suse.cz>
Reported-by:  <urhausen@urifabi.net>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>