[OPTIM] make global.maxpipes default to global.maxconn/4 when not specified

global.maxconn/4 seems to be a good hint for global.maxpipes when that
one must be guessed. If the limit is reached, it's still possible to
set it manually in the configuration.

src/haproxy.c

@@ -566,6 +566,7 @@ void init(int argc, char **argv)
 		global.maxpipes = MAX(nbfe, nbbe);
 		if (global.maxpipes > global.maxconn)
 			global.maxpipes = global.maxconn;
+		global.maxpipes /= 4;
 	}