http2: use the correct function pointer typedef

Fixes gcc-8 picky compiler warnings
Reported-by: Rikard Falkeborn
Bug: #2560
Closes #2568

lib/http.h

@@ -186,9 +186,6 @@ struct HTTP {
 #endif
 };
 
-typedef int (*sending)(void); /* Curl_send */
-typedef int (*recving)(void); /* Curl_recv */
-
 #ifdef USE_NGHTTP2
 /* h2 settings for this connection */
 struct h2settings {
@@ -197,15 +194,14 @@ struct h2settings {
 };
 #endif
 
-
 struct http_conn {
 #ifdef USE_NGHTTP2
 #define H2_BINSETTINGS_LEN 80
   nghttp2_session *h2;
   uint8_t binsettings[H2_BINSETTINGS_LEN];
   size_t  binlen; /* length of the binsettings data */
-  sending send_underlying; /* underlying send Curl_send callback */
-  recving recv_underlying; /* underlying recv Curl_recv callback */
+  Curl_send *send_underlying; /* underlying send Curl_send callback */
+  Curl_recv *recv_underlying; /* underlying recv Curl_recv callback */
   char *inbuf; /* buffer to receive data from underlying socket */
   size_t inbuflen; /* number of bytes filled in inbuf */
   size_t nread_inbuf; /* number of bytes read from in inbuf */

lib/http2.c

@@ -2141,8 +2141,8 @@ CURLcode Curl_http2_switched(struct connectdata *conn,
   if(result)
     return result;
 
-  httpc->recv_underlying = (recving)conn->recv[FIRSTSOCKET];
-  httpc->send_underlying = (sending)conn->send[FIRSTSOCKET];
+  httpc->recv_underlying = conn->recv[FIRSTSOCKET];
+  httpc->send_underlying = conn->send[FIRSTSOCKET];
   conn->recv[FIRSTSOCKET] = http2_recv;
   conn->send[FIRSTSOCKET] = http2_send;
 

lib/urldata.h

@@ -98,6 +98,20 @@
 #include "hash.h"
 #include "splay.h"
 
+/* return the count of bytes sent, or -1 on error */
+typedef ssize_t (Curl_send)(struct connectdata *conn, /* connection data */
+                            int sockindex,            /* socketindex */
+                            const void *buf,          /* data to write */
+                            size_t len,               /* max amount to write */
+                            CURLcode *err);           /* error to return */
+
+/* return the count of bytes read, or -1 on error */
+typedef ssize_t (Curl_recv)(struct connectdata *conn, /* connection data */
+                            int sockindex,            /* socketindex */
+                            char *buf,                /* store data here */
+                            size_t len,               /* max amount to read */
+                            CURLcode *err);           /* error to return */
+
 #include "mime.h"
 #include "imap.h"
 #include "pop3.h"
@@ -704,20 +718,6 @@ struct Curl_handler {
 #define CONNRESULT_NONE 0                /* No extra information. */
 #define CONNRESULT_DEAD (1<<0)           /* The connection is dead. */
 
-/* return the count of bytes sent, or -1 on error */
-typedef ssize_t (Curl_send)(struct connectdata *conn, /* connection data */
-                            int sockindex,            /* socketindex */
-                            const void *buf,          /* data to write */
-                            size_t len,               /* max amount to write */
-                            CURLcode *err);           /* error to return */
-
-/* return the count of bytes read, or -1 on error */
-typedef ssize_t (Curl_recv)(struct connectdata *conn, /* connection data */
-                            int sockindex,            /* socketindex */
-                            char *buf,                /* store data here */
-                            size_t len,               /* max amount to read */
-                            CURLcode *err);           /* error to return */
-
 #ifdef USE_RECV_BEFORE_SEND_WORKAROUND
 struct postponed_data {
   char *buffer;          /* Temporal store for received data during