ext4: fix xattr deadlock

ext4_xattr_set_handle() eventually ends up calling
ext4_mark_inode_dirty() which tries to expand the inode by shifting
the EAs.  This leads to the xattr_sem being downed again and leading
to a deadlock.

This patch makes sure that if ext4_xattr_set_handle() is in the
call-chain, ext4_mark_inode_dirty() will not expand the inode.

Signed-off-by: Kalpak Shah <kalpak.shah@sun.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>