Illumos #3522

3522 zfs module should not allow uninitialized variables
Reviewed by: Sebastien Roy <seb@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
  https://www.illumos.org/issues/3522
  illumos/illumos-gate@d5285cae91

Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting notes:

1. ZFSOnLinux had already addressed many of these issues because of
   its use of -Wall. However, the manner in which they were addressed
   differed. The illumos fixes replace the ones previously made in
   ZFSOnLinux to reduce code differences.

2. Part of the upstream patch made a small change to arc.c that might
   address zfsonlinux/zfs#1334.

3. The initialization of aclsize in zfs_log_create() differs because
   vsecp is a NULL pointer on ZFSOnLinux.

4. The changes to zfs_register_callbacks() were dropped because it
   has diverged and needs to be resynced.

module/zfs/zfs_vnops.c

@@ -2434,7 +2434,7 @@ zfs_setattr(struct inode *ip, vattr_t *vap, int flags, cred_t *cr)
 	vattr_t		oldva;
 	xvattr_t	*tmpxvattr;
 	uint_t		mask = vap->va_mask;
-	uint_t		saved_mask;
+	uint_t		saved_mask = 0;
 	int		trim_mask = 0;
 	uint64_t	new_mode;
 	uint64_t	new_uid, new_gid;