H4 patch

backport from [this fork](https://github.com/philbowles/AsyncTCP)

Author: serek4

src/AsyncTCP.cpp

@@ -562,6 +562,7 @@ AsyncClient::AsyncClient(tcp_pcb* pcb)
 , _rx_since_timeout(0)
 , _ack_timeout(ASYNC_MAX_ACK_TIME)
 , _connect_port(0)
+, _recv_pbuf_flags(0)
 , prev(NULL)
 , next(NULL)
 {
@@ -931,6 +932,8 @@ int8_t AsyncClient::_recv(tcp_pcb* pcb, pbuf* pb, int8_t err) {
             _pb_cb(_pb_cb_arg, this, b);
         } else {
             if(_recv_cb) {
+//              pmb
+                _recv_pbuf_flags = b->flags;
                 _recv_cb(_recv_cb_arg, this, b->payload, b->len);
             }
             if(!_ack_pcb) {

src/AsyncTCP.h

@@ -122,6 +122,7 @@ class AsyncClient {
     void ackPacket(struct pbuf * pb);//ack pbuf from onPacket
     size_t ack(size_t len); //ack data that you have not acked using the method below
     void ackLater(){ _ack_pcb = false; } //will not ack the current packet. Call from onData
+    bool isRecvPush(){ return !!(_recv_pbuf_flags & PBUF_FLAG_PUSH); }
 
     const char * errorToString(int8_t error);
     const char * stateToString();
@@ -168,6 +169,7 @@ class AsyncClient {
     uint32_t _rx_since_timeout;
     uint32_t _ack_timeout;
     uint16_t _connect_port;
+    u8_t _recv_pbuf_flags;
 
     int8_t _close();
     void _free_closed_slot();