CONTRIB: tcploop: add limits.h to fix build issue with some compilers

Just got this while cross-compiling :

tcploop.c: In function 'tcp_recv':
tcploop.c:444:48: error: 'INT_MAX' undeclared (first use in this function)
tcploop.c:444:48: note: each undeclared identifier is reported only once for each function it appears in
diff --git a/contrib/tcploop/tcploop.c b/contrib/tcploop/tcploop.c
index a2ab59e..0334811 100644
--- a/contrib/tcploop/tcploop.c
+++ b/contrib/tcploop/tcploop.c
@@ -39,6 +39,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <limits.h>
 #include <netdb.h>
 #include <poll.h>
 #include <signal.h>