msleep: return EWOULDBLOCK in case of a timeout

bsd/porting/synch.cc

 #include <map>
+#include <errno.h>
 #include "debug.hh"
 #include "drivers/clock.hh"
 #include "sched.hh"
@@ -79,6 +80,11 @@ int synch_port::msleep(void *chan, struct mtx *mtx,
             return ( (t.expired()) || (wait._awake) );
         });
 
+        // msleep timeout
+        if (!wait._awake) {
+            return (EWOULDBLOCK);
+        }
+
     } else {
 
         sched::thread::wait_until(wait_lock, [&] {