epoll_create: fail with EINVAL if size is non-positive

This is a part of the interface contract defined in the Linux man
page (official for a Linux-specific interface) and asserted by test
cases in the Linux Test Project (LTP).

src/linux/epoll.c

@@ -5,6 +5,7 @@
 
 int epoll_create(int size)
 {
+	if (size<=0) return __syscall_ret(-EINVAL);
 	return epoll_create1(0);
 }