lavf/network: add a ff_log_net_error function.

add a ff_log_net_error function for error log.
Signed-off-by: Jun Zhao <mypopydev@gmail.com>

libavformat/network.c

@@ -346,3 +346,10 @@ int ff_http_match_no_proxy(const char *no_proxy, const char *hostname)
     av_free(buf);
     return ret;
 }
+
+void ff_log_net_error(void *ctx, int level, const char* prefix)
+{
+    char errbuf[100];
+    av_strerror(ff_neterrno(), errbuf, sizeof(errbuf));
+    av_log(ctx, level, "%s: %s\n", prefix, errbuf);
+}

libavformat/network.h

@@ -304,4 +304,6 @@ int ff_http_match_no_proxy(const char *no_proxy, const char *hostname);
 
 int ff_socket(int domain, int type, int protocol);
 
+void ff_log_net_error(void *ctx, int level, const char* prefix);
+
 #endif /* AVFORMAT_NETWORK_H */