osdep.c: Fix accept4 fallback

Commit 3a03bfa5 added a fallback in case the Linux kernel running qemu is older
than the kernel of the build system. Unfortunately, v1 was committed instead of
v2, so the code has a bug that was revealed in the review (checking for the
wrong error code).
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

osdep.c

@@ -297,7 +297,7 @@ int qemu_accept(int s, struct sockaddr *addr, socklen_t *addrlen)
 
 #ifdef CONFIG_ACCEPT4
     ret = accept4(s, addr, addrlen, SOCK_CLOEXEC);
-    if (ret != -1 || errno != EINVAL) {
+    if (ret != -1 || errno != ENOSYS) {
         return ret;
     }
 #endif