Add DTLS test to check 6 byte record ctr is cmp

Add a test to ssl-opt.sh to ensure that in DTLS a 6 byte record counter
is compared in ssl_check_ctr_renegotiate() instead of a 8 byte one as in
the TLS case. Because currently there are no testing facilities to check
that renegotiation routines are triggered after X number of input/output
messages, the test consists on setting a renegotiation period that
cannot be represented in 6 bytes, but whose least-significant byte is 2.
If the library behaves correctly, the renegotiation routines will be
executed after two exchanged.

tests/ssl-opt.sh

@@ -1601,6 +1601,19 @@ run_test    "Renegotiation: DTLS, server-initiated" \
             -s "=> renegotiate" \
             -s "write hello request"
 
+run_test    "Renegotiation: DTLS, renego_period overflow" \
+            "$P_SRV debug_level=3 dtls=1 exchanges=4 renegotiation=1 renego_period=18446462598732840962 auth_mode=optional" \
+            "$P_CLI debug_level=3 dtls=1 exchanges=4 renegotiation=1" \
+            0 \
+            -c "client hello, adding renegotiation extension" \
+            -s "received TLS_EMPTY_RENEGOTIATION_INFO" \
+            -s "found renegotiation extension" \
+            -s "server hello, secure renegotiation extension" \
+            -s "record counter limit reached: renegotiate" \
+            -c "=> renegotiate" \
+            -s "=> renegotiate" \
+            -s "write hello request" \
+
 requires_gnutls
 run_test    "Renegotiation: DTLS, gnutls server, client-initiated" \
             "$G_SRV -u --mtu 4096" \