add back x32 bits/socket.h defining time-related socket options

these definitions are merely copied from the top-level sys/socket.h,
so there is no functional change at this time. however, the top-level
definitions will change to use the time64 "_NEW" versions on 32-bit
archs when time_t is switched over to 64-bit. this commit ensures that
change will be suppressed on x32.

arch/x32/bits/socket.h

@@ -0,0 +1,5 @@
+#define SO_RCVTIMEO     20
+#define SO_SNDTIMEO     21
+#define SO_TIMESTAMP    29
+#define SO_TIMESTAMPNS  35
+#define SO_TIMESTAMPING 37