sd-ndisc.c: Move Router Solicitation sending after timer computaion

Move ICMPv6 Router Solicitation sending after timer computation so
that timers are already set up when the packet is being sent. This
makes it possible to create a test that inspects Router
Solicitation timer values when the Router Solicitation is sent out
on the network.

Author: pfl

src/libsystemd-network/sd-ndisc.c

@@ -281,12 +281,6 @@ static int ndisc_timeout(sd_event_source *s, uint64_t usec, void *userdata) {
         assert(nd);
         assert(nd->event);
 
-        r = icmp6_send_router_solicitation(nd->fd, &nd->mac_addr);
-        if (r < 0) {
-                log_ndisc_errno(r, "Error sending Router Solicitation: %m");
-                goto fail;
-        }
-
         assert_se(sd_event_now(nd->event, clock_boottime_or_monotonic(), &time_now) >= 0);
 
         nd->timeout_event_source = sd_event_source_unref(nd->timeout_event_source);
@@ -319,6 +313,12 @@ static int ndisc_timeout(sd_event_source *s, uint64_t usec, void *userdata) {
                 goto fail;
         }
 
+        r = icmp6_send_router_solicitation(nd->fd, &nd->mac_addr);
+        if (r < 0) {
+                log_ndisc_errno(r, "Error sending Router Solicitation: %m");
+                goto fail;
+        }
+
         log_ndisc("Sent Router Solicitation, next solicitation in %s",
                   format_timespan(time_string, FORMAT_TIMESPAN_MAX,
                                   nd->retransmit_time, USEC_PER_SEC));