Fix some more socket bugs

- The functions that return a sockaddr now do so the same way the Linux
  Kernel does across platforms, e.g. getpeername(), accept4()

- Socket system calls on Windows will now only check for interrupts when
  a blocking operation needs to be performed.

- Write tests for recvfrom() system call

libc/sock/wsablock.c

@@ -40,7 +40,7 @@ textwindows int __wsablock(struct Fd *fd, struct NtOverlapped *overlapped,
                            uint32_t *flags, bool restartable,
                            uint32_t timeout) {
   int e, rc;
-  uint32_t i, got = -666;
+  uint32_t i, got;
   if (WSAGetLastError() != kNtErrorIoPending) {
     NTTRACE("sock i/o failed %s", strerror(errno));
     return __winsockerr();