zpool import speedup

*** 631,641 ****
          zilog_t *zilog;
          zil_header_t *zh;
          objset_t *os;
          int error;
  
!         error = dmu_objset_own(osname, DMU_OST_ANY, B_FALSE, FTAG, &os);
          if (error != 0) {
                  cmn_err(CE_WARN, "can't open objset for %s", osname);
                  return (0);
          }
  
--- 631,641 ----
          zilog_t *zilog;
          zil_header_t *zh;
          objset_t *os;
          int error;
  
!         error = dmu_objset_own_nolock(osname, DMU_OST_ANY, B_FALSE, FTAG, &os);
          if (error != 0) {
                  cmn_err(CE_WARN, "can't open objset for %s", osname);
                  return (0);
          }
  
*** 689,699 ****
          blkptr_t *bp;
          int error;
  
          ASSERT(tx == NULL);
  
!         error = dmu_objset_hold(osname, FTAG, &os);
          if (error != 0) {
                  cmn_err(CE_WARN, "can't open objset for %s", osname);
                  return (0);
          }
  
--- 689,699 ----
          blkptr_t *bp;
          int error;
  
          ASSERT(tx == NULL);
  
!         error = dmu_objset_hold_nolock(osname, FTAG, &os);
          if (error != 0) {
                  cmn_err(CE_WARN, "can't open objset for %s", osname);
                  return (0);
          }