Move ssl_update_in_pointers() to after record hdr parsing

Previously, ssl_update_in_pointers() ensured that the in_xxx pointers
in the SSL context are set to their default state so that the record
header parsing function ssl_parse_record_header() could make use of them.
By now, the latter is independent of these pointers, so they don't need
to be setup before calling ssl_parse_record_header() anymore.
However, other parts of the messaging stack might still depend on it
(to be studied), and hence this commit does not yet reomve
ssl_update_in_pointers() entirely.
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index d200304..128a40e 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -5994,11 +5994,6 @@
         return( ret );
 #endif /* MBEDTLS_SSL_PROTO_DTLS */
 
-    /* Reset in pointers to default state for TLS/DTLS records,
-     * assuming no CID and no offset between record content and
-     * record plaintext. */
-    ssl_update_in_pointers( ssl );
-
     /* Ensure that we have enough space available for the default form
      * of TLS / DTLS record headers (5 Bytes for TLS, 13 Bytes for DTLS,
      * with no space for CIDs counted in). */
@@ -6028,6 +6023,11 @@
             if( ret == MBEDTLS_ERR_SSL_UNEXPECTED_RECORD )
             {
 #if defined(MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE) && defined(MBEDTLS_SSL_SRV_C)
+                /* Reset in pointers to default state for TLS/DTLS records,
+                 * assuming no CID and no offset between record content and
+                 * record plaintext. */
+                ssl_update_in_pointers( ssl );
+
                 /* Setup internal message pointers from record structure. */
                 ssl->in_msgtype = rec.type;
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
@@ -6067,6 +6067,11 @@
         }
     }
 
+    /* Reset in pointers to default state for TLS/DTLS records,
+     * assuming no CID and no offset between record content and
+     * record plaintext. */
+    ssl_update_in_pointers( ssl );
+
     /* Setup internal message pointers from record structure. */
     ssl->in_msgtype = rec.type;
 #if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)