Corral the last setsockopt() call into one place.

adsbus/incoming.c

@@ -110,8 +110,7 @@ static void incoming_listen(struct incoming *incoming) {
 		incoming->peer.fd = socket(addr->ai_family, addr->ai_socktype | SOCK_CLOEXEC, addr->ai_protocol);
 		assert(incoming->peer.fd >= 0);
 
-		int optval = 1;
-		setsockopt(incoming->peer.fd, SOL_SOCKET, SO_REUSEPORT, &optval, sizeof(optval));
+		socket_pre_bind_init(incoming->peer.fd);
 
 		if (bind(incoming->peer.fd, addr->ai_addr, addr->ai_addrlen) != 0) {
 			fprintf(stderr, "I %s: Failed to bind to %s/%s: %s\n", incoming->id, hbuf, sbuf, strerror(errno));

adsbus/socket.c

@@ -7,6 +7,11 @@
 
 #include "socket.h"
 
+void socket_pre_bind_init(int fd) {
+	int optval = 1;
+	assert(!setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &optval, sizeof(optval)));
+}
+
 void socket_bound_init(int fd) {
 	int qlen = 5;
 	assert(!setsockopt(fd, SOL_TCP, TCP_FASTOPEN, &qlen, sizeof(qlen)));

adsbus/socket.h

@@ -1,4 +1,5 @@
 #pragma once
 
+void socket_pre_bind_init(int);
 void socket_bound_init(int);
 void socket_connected_init(int);