Won't compile under Core 2.4.0-rc2

[Pablo2048]

ESPAsyncTCP won't compile under ESP8266 Core 2.4.0-rc2 with this error:

ESPAsyncTCP.cpp:77:28: error: invalid conversion from 'int8_t (*)(void*, tcp_pcb*, pbuf*, int8_t) {aka signed char (*)(void*, tcp_pcb*, pbuf*, signed char)}' to 'tcp_recv_fn {aka long int (*)(void*, tcp_pcb*, pbuf*, long int)}' [-fpermissive]
     tcp_recv(_pcb, &_s_recv);

It seems like conflict with lwip v2 implementation to me...

[majklovec]

#56