extmod/modtls_mbedtls: Add a thread-global ptr for current SSL context.

This is necessary for mbedTLS callbacks that do not carry any user state,
so those callbacks can be customised per SSL context.

Signed-off-by: iabdalkader <i.abdalkader@gmail.com>

py/mpconfig.h

@@ -1814,6 +1814,11 @@ typedef double mp_float_t;
 #define MICROPY_PY_SSL_FINALISER (MICROPY_ENABLE_FINALISER)
 #endif
 
+// Whether to add a root pointer for the current ssl object
+#ifndef MICROPY_PY_SSL_MBEDTLS_NEED_ACTIVE_CONTEXT
+#define MICROPY_PY_SSL_MBEDTLS_NEED_ACTIVE_CONTEXT (MICROPY_PY_SSL_ECDSA_SIGN_ALT)
+#endif
+
 // Whether to provide the "vfs" module
 #ifndef MICROPY_PY_VFS
 #define MICROPY_PY_VFS (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES && MICROPY_VFS)

py/mpstate.h

@@ -293,6 +293,10 @@ typedef struct _mp_state_thread_t {
     bool prof_callback_is_executing;
     struct _mp_code_state_t *current_code_state;
     #endif
+
+    #if MICROPY_PY_SSL_MBEDTLS_NEED_ACTIVE_CONTEXT
+    struct _mp_obj_ssl_context_t *tls_ssl_context;
+    #endif
 } mp_state_thread_t;
 
 // This structure combines the above 3 structures.