mbedtls_ssl_handshake_params: move group_list earlier to save code size

Placing group_list earlier seems to help significantly, not just as a matter
of placing it in the 128-element (512-byte) access window.

Results (arm-none-eabi-gcc 7.3.1, build_arm_none_eabi_gcc_m0plus build):
library/ssl_cli.o: 19559 -> 19551 (diff: 8)
library/ssl_msg.o: 24690 -> 24674 (diff: 16)
library/ssl_srv.o: 20418 -> 20406 (diff: 12)
library/ssl_tls.o: 20555 -> 20519 (diff: 36)
library/ssl_tls13_client.o: 7244 -> 7240 (diff: 4)
library/ssl_tls13_generic.o: 4693 -> 4697 (diff: -4)

Results (same architecture, config-suite-b.h + MBEDTLS_ECDH_LEGACY_CONTEXT +
MBEDTLS_ECP_RESTARTABLE):
library/ssl_cli.o: 2864 -> 2860 (diff: 4)
library/ssl_tls.o: 6566 -> 6546 (diff: 20)

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 6af125f..8a882f2 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -552,6 +552,10 @@
     unsigned char retransmit_state;     /*!<  Retransmission state           */
 #endif
 
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+    unsigned char group_list_heap_allocated;
+#endif
+
 #if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
     uint8_t ecrs_enabled;               /*!< Handshake supports EC restart? */
     mbedtls_x509_crt_restart_ctx ecrs_ctx;  /*!< restart context            */
@@ -587,6 +591,10 @@
     mbedtls_ssl_sig_hash_set_t hash_algs;             /*!<  Set of suitable sig-hash pairs */
 #endif
 
+#if !defined(MBEDTLS_DEPRECATED_REMOVED)
+    const uint16_t *group_list;
+#endif
+
 #if defined(MBEDTLS_DHM_C)
     mbedtls_dhm_context dhm_ctx;                /*!<  DHM key exchange        */
 #endif
@@ -802,11 +810,6 @@
      * The library does not use it internally. */
     void *user_async_ctx;
 #endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
-
-#if !defined(MBEDTLS_DEPRECATED_REMOVED)
-    const uint16_t *group_list;
-    unsigned char group_list_heap_allocated;
-#endif
 };
 
 typedef struct mbedtls_ssl_hs_buffer mbedtls_ssl_hs_buffer;