Enable the load-balance-sockets configuration

Previously, HAVE_SO_REUSEPORT_LB has been defined only in the private
netmgr-int.h header file, making the configuration of load balanced
sockets inoperable.

Move the missing HAVE_SO_REUSEPORT_LB define the isc/netmgr.h and add
missing isc_nm_getloadbalancesockets() implementation.

bin/named/config.c

@@ -20,6 +20,7 @@
 #include <isc/buffer.h>
 #include <isc/log.h>
 #include <isc/mem.h>
+#include <isc/netmgr.h>
 #include <isc/parseint.h>
 #include <isc/region.h>
 #include <isc/result.h>

bin/named/server.c

@@ -39,6 +39,7 @@
 #include <isc/httpd.h>
 #include <isc/lex.h>
 #include <isc/meminfo.h>
+#include <isc/netmgr.h>
 #include <isc/nonce.h>
 #include <isc/parseint.h>
 #include <isc/portset.h>

lib/isc/include/isc/netmgr.h

@@ -13,12 +13,21 @@
 
 #pragma once
 
+#include <unistd.h>
+
 #include <isc/mem.h>
 #include <isc/region.h>
 #include <isc/result.h>
 #include <isc/tls.h>
 #include <isc/types.h>
 
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#if defined(SO_REUSEPORT_LB) || (defined(SO_REUSEPORT) && defined(__linux__))
+#define HAVE_SO_REUSEPORT_LB 1
+#endif
+
 /*
  * Replacement for isc_sockettype_t provided by socket.h.
  */

lib/isc/netmgr/netmgr-int.h

@@ -111,10 +111,6 @@ STATIC_ASSERT(ISC_NETMGR_TCP_RECVBUF_SIZE <= ISC_NETMGR_RECVBUF_SIZE,
  */
 #define NM_MAXSEG (1280 - 20 - 40)
 
-#if defined(SO_REUSEPORT_LB) || (defined(SO_REUSEPORT) && defined(__linux__))
-#define HAVE_SO_REUSEPORT_LB 1
-#endif
-
 /*
  * Define NETMGR_TRACE to activate tracing of handles and sockets.
  * This will impair performance but enables us to quickly determine,

lib/isc/netmgr/netmgr.c

@@ -578,6 +578,13 @@ isc_nm_setnetbuffers(isc_nm_t *mgr, int32_t recv_tcp, int32_t send_tcp,
 	atomic_store(&mgr->send_udp_buffer_size, send_udp);
 }
 
+bool
+isc_nm_getloadbalancesockets(isc_nm_t *mgr) {
+	REQUIRE(VALID_NM(mgr));
+
+	return (mgr->load_balance_sockets);
+}
+
 void
 isc_nm_setloadbalancesockets(isc_nm_t *mgr, bool enabled) {
 	REQUIRE(VALID_NM(mgr));