adding UDP setBlock option

Changelog

@@ -1,3 +1,6 @@
+2019-12-29:
+- added: UDP reads can be set to non blocked mode.
+
 2019-07-21:
 - fixed: compile will work with older versions of SSL.
 

UDPTCPNetwork.h

@@ -48,6 +48,7 @@ public:
 
 	int Listen(int port);
 
+	int SetBlocked(int bl);
 	long int ReadTimeout(string *srcaddr, char *buffer, long int len, int timeout_ms);
 	long int Read(string *srcaddr, char *buffer, long int len);
 	long int Write(string destaddr, char *buffer, long int len);

udp.cc

@@ -6,6 +6,7 @@
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
+#include <fcntl.h>
 #include <netdb.h>
 #include <stdio.h>
 #include <unistd.h> /* close() */
@@ -93,6 +94,16 @@ long int UDP::Read(string *source, char *buffer, long int len) {
 }
 
 
+int UDP::SetBlocked(int bl) {
+	int flags = fcntl(sock, F_GETFL, 0);
+
+	if (bl) flags &= ~O_NONBLOCK;
+	else flags |= O_NONBLOCK;
+
+	return fcntl(sock, F_SETFL, flags | O_NONBLOCK);
+}
+
+
 long int UDP::Write(string destaddr, char *buffer, long int len) {
 	int s;
 	int addrlen = sizeof (struct sockaddr_in);