Convert another parser of struct timespec to new mpers infrastructure

* print_time.c (sprint_timespec): New mpers printer.
* defs.h (TIMESPEC_TEXT_BUFSIZE): Update.
(sprint_timespec): Remove.
* time.c (sprint_timespec): Remove.
* net.c (sys_recvmmsg): Update callers.
* poll.c (decode_poll_exiting): Likewise.
diff --git a/poll.c b/poll.c
index bf9707c..4c3f19e 100644
--- a/poll.c
+++ b/poll.c
@@ -169,12 +169,11 @@
 
 	*outptr = '\0';
 	if (pts) {
-		char tmbuf[TIMESPEC_TEXT_BUFSIZE];
+		const char *str = sprint_timespec(tcp, pts);
 
-		sprint_timespec(tmbuf, tcp, pts);
-		if (outptr + sizeof(", left ") + strlen(tmbuf) < end_outstr) {
+		if (outptr + sizeof(", left ") + strlen(str) < end_outstr) {
 			outptr = stpcpy(outptr, outptr == outstr ? "left " : ", left ");
-			outptr = stpcpy(outptr, tmbuf);
+			outptr = stpcpy(outptr, str);
 		} else {
 			outptr = stpcpy(outptr, ", ...");
 		}