Merge in_hsfraglen with badmac_seen_or_in_hsfraglen

In the `mbedtls_ssl_context` structure, merge the field `in_hsfraglen` into
`badmac_seen_or_in_hsfraglen`. This restores the ABI of `libmbedtls` as it
was in Mbed TLS 3.6.0 through 3.6.2.

The field `badmac_seen_or_in_hsfraglen` (formerly `badmac_seen`) was only
used for DTLS (despite being present in non-DTLS builds), and the field
`in_hsfraglen` was only used in non-DTLS TLS. Therefore the two values can
be stored in the same field.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index f8cd74b..8428b38 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1488,7 +1488,7 @@
     ssl->in_msgtype = 0;
     ssl->in_msglen  = 0;
     ssl->in_hslen   = 0;
-    ssl->in_hsfraglen = 0;
+    ssl->badmac_seen_or_in_hsfraglen = 0;
     ssl->keep_current_message = 0;
     ssl->transform_in  = NULL;