w32: Fix build with new net bridge code

Commit a7c36ee4920ea3acc227a0248dd161693f207357 added code for a net
bridge and explicitly said that "this is very Linux centric".

Indeed, compilation failed for w32, so the bridge code is now
conditional. Hosts which don't support it can simply remove the
definition of CONFIG_NET_BRIDGE.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

net.c

@@ -38,6 +38,11 @@
 #include "hw/qdev.h"
 #include "iov.h"
 
+/* Net bridge is currently not supported for W32. */
+#if !defined(_WIN32)
+# define CONFIG_NET_BRIDGE
+#endif
+
 static QTAILQ_HEAD(, VLANState) vlans;
 static QTAILQ_HEAD(, VLANClientState) non_vlan_clients;
 
@@ -952,10 +957,12 @@ static const struct {
                 .type = QEMU_OPT_STRING,
                 .help = "script to shut down the interface",
             }, {
+#ifdef CONFIG_NET_BRIDGE
                 .name = "helper",
                 .type = QEMU_OPT_STRING,
                 .help = "command to execute to configure bridge",
             }, {
+#endif
                 .name = "sndbuf",
                 .type = QEMU_OPT_SIZE,
                 .help = "send buffer limit"
@@ -1057,6 +1064,7 @@ static const struct {
             { /* end of list */ }
         },
     },
+#ifdef CONFIG_NET_BRIDGE
     [NET_CLIENT_TYPE_BRIDGE] = {
         .type = "bridge",
         .init = net_init_bridge,
@@ -1074,6 +1082,7 @@ static const struct {
             { /* end of list */ }
         },
     },
+#endif /* CONFIG_NET_BRIDGE */
 };
 
 int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
@@ -1090,14 +1099,16 @@ int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
 
     if (is_netdev) {
         if (strcmp(type, "tap") != 0 &&
+#ifdef CONFIG_NET_BRIDGE
+            strcmp(type, "bridge") != 0 &&
+#endif
 #ifdef CONFIG_SLIRP
             strcmp(type, "user") != 0 &&
 #endif
 #ifdef CONFIG_VDE
             strcmp(type, "vde") != 0 &&
 #endif
-            strcmp(type, "socket") != 0 &&
-            strcmp(type, "bridge") != 0) {
+            strcmp(type, "socket") != 0) {
             qerror_report(QERR_INVALID_PARAMETER_VALUE, "type",
                           "a netdev backend type");
             return -1;
@@ -1161,13 +1172,15 @@ static int net_host_check_device(const char *device)
 {
     int i;
     const char *valid_param_list[] = { "tap", "socket", "dump"
+#ifdef CONFIG_NET_BRIDGE
+                                       , "bridge"
+#endif
 #ifdef CONFIG_SLIRP
                                        ,"user"
 #endif
 #ifdef CONFIG_VDE
                                        ,"vde"
 #endif
-                                       , "bridge"
     };
     for (i = 0; i < sizeof(valid_param_list) / sizeof(char *); i++) {
         if (!strncmp(valid_param_list[i], device,