Add guards for closed socket in net.c
This is particularly problematic when calling FD_SET( -1, ... ), but let's
check it in all functions.
This was introduced with the new API and the fact the net_free() now sets the
internal fd to -1 in order to mark it as closed: now using this information.
diff --git a/include/mbedtls/net.h b/include/mbedtls/net.h
index 19746e5..1c49763 100644
--- a/include/mbedtls/net.h
+++ b/include/mbedtls/net.h
@@ -45,6 +45,7 @@
#define MBEDTLS_ERR_NET_CONN_RESET -0x0050 /**< Connection was reset by peer. */
#define MBEDTLS_ERR_NET_UNKNOWN_HOST -0x0052 /**< Failed to get an IP address for the given hostname. */
#define MBEDTLS_ERR_NET_BUFFER_TOO_SMALL -0x0043 /**< Buffer is too small to hold the data. */
+#define MBEDTLS_ERR_NET_INVALID_CONTEXT -0x0045 /**< The context is invalid, eg because it was free()ed. */
#define MBEDTLS_NET_LISTEN_BACKLOG 10 /**< The backlog that listen() should use. */