OpenZFS 8063 - verify that we do not attempt to access inactive txg

Authored by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

A standard practice in ZFS is to keep track of "per-txg" state. Any of
the 3 active TXG's (open, quiescing, syncing) can have different values
for this state. We should assert that we do not attempt to modify other
(inactive) TXG's.

Porting Notes:
- ASSERTV added to txg_sync_waiting() for unused variable.

OpenZFS-issue: https://www.illumos.org/issues/8063
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/01acb46
Closes #6109

module/zfs/zil.c

@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2017 by Delphix. All rights reserved.
  * Copyright (c) 2014 Integros [integros.com]
  */
 
@@ -109,16 +109,6 @@ static void zil_async_to_sync(zilog_t *zilog, uint64_t foid);
 #define	LWB_EMPTY(lwb) ((BP_GET_LSIZE(&lwb->lwb_blk) - \
     sizeof (zil_chain_t)) == (lwb->lwb_sz - lwb->lwb_nused))
 
-
-/*
- * ziltest is by and large an ugly hack, but very useful in
- * checking replay without tedious work.
- * When running ziltest we want to keep all itx's and so maintain
- * a single list in the zl_itxg[] that uses a high txg: ZILTEST_TXG
- * We subtract TXG_CONCURRENT_STATES to allow for common code.
- */
-#define	ZILTEST_TXG (UINT64_MAX - TXG_CONCURRENT_STATES)
-
 static int
 zil_bp_compare(const void *x1, const void *x2)
 {