4047 panic from dbuf_free_range() from dmu_free_object() while doing zfs receive
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>

@@ -613,10 +613,11 @@
          * any level-0 dbufs that will be completely freed.  Therefore we must
          * exercise care to not read or count the first and last blocks
          * if they are blocksize-aligned.
          */
         if (dn->dn_datablkshift == 0) {
+                if (off != 0 || len < dn->dn_datablksz)
                 dmu_tx_count_write(txh, off, len);
         } else {
                 /* first block will be modified if it is not aligned */
                 if (!IS_P2ALIGNED(off, 1 << dn->dn_datablkshift))
                         dmu_tx_count_write(txh, off, 1);