Update error codes listed in the net_sockets documentation

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/net_sockets.h b/include/mbedtls/net_sockets.h
index 702e93f..319f4be 100644
--- a/include/mbedtls/net_sockets.h
+++ b/include/mbedtls/net_sockets.h
@@ -124,6 +124,7 @@
  *
  * \return         0 if successful, or one of:
  *                      MBEDTLS_ERR_NET_SOCKET_FAILED,
+ *                      MBEDTLS_ERR_NET_UNKNOWN_HOST,
  *                      MBEDTLS_ERR_NET_BIND_FAILED,
  *                      MBEDTLS_ERR_NET_LISTEN_FAILED
  *
@@ -143,6 +144,8 @@
  *                  can be NULL if client_ip is null
  *
  * \return          0 if successful, or
+ *                  MBEDTLS_ERR_NET_SOCKET_FAILED,
+ *                  MBEDTLS_ERR_NET_BIND_FAILED,
  *                  MBEDTLS_ERR_NET_ACCEPT_FAILED, or
  *                  MBEDTLS_ERR_NET_BUFFER_TOO_SMALL if buf_size is too small,
  *                  MBEDTLS_ERR_SSL_WANT_READ if bind_fd was set to
@@ -250,10 +253,11 @@
  * \param timeout  Maximum number of milliseconds to wait for data
  *                 0 means no timeout (wait forever)
  *
- * \return         the number of bytes received,
- *                 or a non-zero error code:
- *                 MBEDTLS_ERR_SSL_TIMEOUT if the operation timed out,
+ * \return         The number of bytes received if successful.
+ *                 MBEDTLS_ERR_SSL_TIMEOUT if the operation timed out.
  *                 MBEDTLS_ERR_SSL_WANT_READ if interrupted by a signal.
+ *                 Another negative error code (MBEDTLS_ERR_NET_xxx)
+ *                 for other failures.
  *
  * \note           This function will block (until data becomes available or
  *                 timeout is reached) even if the socket is set to