6220 memleak in l2arc on debug build

@@ -1299,10 +1299,17 @@
                  * might try to be accessed, even though it was removed.
                  */
                 VERIFY(!HDR_L2_WRITING(hdr));
                 VERIFY3P(hdr->b_l1hdr.b_tmp_cdata, ==, NULL);
 
+#ifdef ZFS_DEBUG
+                if (hdr->b_l1hdr.b_thawed != NULL) {
+                        kmem_free(hdr->b_l1hdr.b_thawed, 1);
+                        hdr->b_l1hdr.b_thawed = NULL;
+                }
+#endif
+
                 nhdr->b_flags &= ~ARC_FLAG_HAS_L1HDR;
         }
         /*
          * The header has been reallocated so we need to re-insert it into any
          * lists it was on.