_libssh2_packet_add: SSH_MSG_CHANNEL_REQUEST default to want_reply

RFC4254 says the default 'want_reply' is TRUE but the code defaulted to
FALSE. Now changed.

Fixes #233

src/packet.c

@@ -751,7 +751,7 @@ _libssh2_packet_add(LIBSSH2_SESSION * session, unsigned char *data,
             if(datalen >= 9) {
                 uint32_t channel = _libssh2_ntohu32(data + 1);
                 uint32_t len = _libssh2_ntohu32(data + 5);
-                unsigned char want_reply = 0;
+                unsigned char want_reply = 1;
 
                 if(len < (datalen - 10))
                     want_reply = data[9 + len];