Change ASSERT(!"...") to cmn_err(CE_PANIC, ...)

There are a handful of ASSERT(!"...")'s throughout the code base for
cases which should be impossible.  This patch converts them to use
cmn_err(CE_PANIC, ...) to ensure they are always enabled and so that
additional debugging is logged if they were to occur.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1445

module/zcommon/zfs_deleg.c

@@ -227,7 +227,7 @@ zfs_deleg_whokey(char *attr, zfs_deleg_who_type_t type,
 		    ZFS_DELEG_FIELD_SEP_CHR);
 		break;
 	default:
-		ASSERT(!"bad zfs_deleg_who_type_t");
+		cmn_err(CE_PANIC, "bad zfs_deleg_who_type_t %d", type);
 	}
 }