client: include winsock headers on WIN32

On Windows, socket declarations reside in winsock.h and ws2tcpip.h.
The POSIX headers sys/socket.h etc. are not available.

src/client.c

@@ -31,11 +31,17 @@
 
 #include <glib.h>
 #include <assert.h>
+#include <unistd.h>
+#include <string.h>
+
+#ifdef WIN32
+#include <ws2tcpip.h>
+#include <winsock.h>
+#else
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
-#include <unistd.h>
-#include <string.h>
+#endif
 
 #undef G_LOG_DOMAIN
 #define G_LOG_DOMAIN "client"

src/client.h

@@ -23,9 +23,9 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdarg.h>
-#include <sys/socket.h>
 
 struct client;
+struct sockaddr;
 
 void client_manager_init(void);
 void client_manager_deinit(void);