ipdbg-la: Fix two compiler warnings on Windows.

ipdbg-la: Fix two compiler warnings on Windows.

This is happening because the send() and recv() functions
have different prototypes on POSIX and Windows. Using the casts
is required on Windows and doesn't hurt on POSIX systems.

  [...]/protocol.c: In function 'tcp_send':
  [...]/protocol.c:161:26: warning: pointer targets in passing argument 2 of 'send' differ in signedness [-Wpointer-sign]
    out = send(tcp->socket, buf, len, 0);
                            ^
  In file included from [...]/protocol.c:24:0:
  [...]/include/winsock2.h:997:34: note: expected 'const char *' but argument is of type 'const uint8_t * {aka const unsigned char *}'
     WINSOCK_API_LINKAGE int WSAAPI send(SOCKET s,const char *buf,int len,int flags);
                                    ^
  [...]/protocol.c: In function 'ipdbg_la_tcp_receive':
  [...]/protocol.c:201:32: warning: pointer targets in passing argument 2 of 'recv' differ in signedness [-Wpointer-sign]
      int len = recv(tcp->socket, buf, 1, 0);
                                  ^
  In file included from [...]/protocol.c:24:0:
  [...]/include/winsock2.h:992:34: note: expected 'char *' but argument is of type 'uint8_t * {aka unsigned char *}'
     WINSOCK_API_LINKAGE int WSAAPI recv(SOCKET s,char *buf,int len,int flags);
                                    ^