Replace sys/time.h with <chrono> for portability/modernization.

lib/packet_pad_impl.cc

@@ -16,9 +16,9 @@
  */
 #include "packet_pad_impl.h"
 
+#include <chrono>
 #include <gnuradio/io_signature.h>
 #include <iostream>
-#include <sys/time.h>
 #ifdef FOO_UHD
 #include <uhd/types/time_spec.hpp>
 #endif
@@ -58,9 +58,12 @@ packet_pad_impl::add_sob(uint64_t item) {
 	#ifdef FOO_UHD
 	if(d_delay) {
 		static const pmt::pmt_t time_key = pmt::string_to_symbol("tx_time");
-		struct timeval t;
-		gettimeofday(&t, NULL);
-		uhd::time_spec_t now = uhd::time_spec_t(t.tv_sec + t.tv_usec / 1000000.0)
+		double t_now(
+			std::chrono::duration<double>(std::chrono::system_clock::now()
+                .time_since_epoch()
+            ).count()
+        );
+		uhd::time_spec_t now = uhd::time_spec_t(t_now)
 			+ uhd::time_spec_t(d_delay_sec);
 
 		const pmt::pmt_t time_value = pmt::make_tuple(