Linux 3.3 compat, iops->create()/mkdir()/mknod()

The mode argument of iops->create()/mkdir()/mknod() was changed from
an 'int' to a 'umode_t'.  To prevent a compiler warning an autoconf
check was added to detect the API change and then correctly set a
zpl_umode_t typedef.  There is no functional change.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #701

module/zfs/zpl_ctldir.c

@@ -300,7 +300,7 @@ zpl_snapdir_rmdir(struct inode *dip, struct dentry *dentry)
 }
 
 static int
-zpl_snapdir_mkdir(struct inode *dip, struct dentry *dentry, int mode)
+zpl_snapdir_mkdir(struct inode *dip, struct dentry *dentry, zpl_umode_t mode)
 {
 	cred_t *cr = CRED();
 	vattr_t *vap;