linux: Fix missing __convert_scm_timestamps (BZ #28860)

Commit 948ce73b31 made recvmsg/recvmmsg to always call
__convert_scm_timestamps for 64 bit time_t symbol, so adjust it to
always build it for __TIMESIZE != 64.

It fixes build for architecture with 32 bit time_t support when
configured with minimum kernel of 5.1.

sysdeps/unix/sysv/linux/convert_scm_timestamps.c

@@ -16,9 +16,9 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <kernel-features.h>
+#include <bits/timesize.h>
 
-#ifndef __ASSUME_TIME64_SYSCALLS
+#if __TIMESIZE != 64
 # include <stdint.h>
 # include <string.h>
 # include <sys/socket.h>