Fix potential NULL dereference
We document that either of recv or recv_timeout may be NULL, but for TLS we
always used recv... Thanks Coverity for catching that.
(Not remotely trigerrable: local configuration.)
Also made me notice net_recv_timeout didn't do its job properly.
diff --git a/include/mbedtls/net.h b/include/mbedtls/net.h
index ed2d5d3..92f94c0 100644
--- a/include/mbedtls/net.h
+++ b/include/mbedtls/net.h
@@ -178,6 +178,7 @@
* \param buf The buffer to write to
* \param len Maximum length of the buffer
* \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: