Fix warning anywhere netwrap.h is included before sockwrap.h

sbbs3/../xpdev/netwrap.h:45:27: warning: 'parseIPv6Address' has C-linkage specified, but returns incomplete type 'struct in6_addr' which could be incompatible with C [-Wreturn-type-c-linkage]
DLLEXPORT struct in6_addr parseIPv6Address(const char*);
                          ^

src/xpdev/netwrap.h

@@ -29,6 +29,8 @@
 #if defined(_WIN32)
 	#include <winsock2.h>
 	#include <ws2tcpip.h>	// struct in6_addr
+#else
+	#include <netinet/in.h>
 #endif
 
 #define IPv4_LOCALHOST	0x7f000001U	/* 127.0.0.1 */