Use enc_flags when deciding protocol variations.

Use the enc_flags field to determine whether we should use explicit IV,
signature algorithms or SHA256 default PRF instead of hard coding which
versions support each requirement.
(cherry picked from commit cbd64894ec)

Conflicts:

	ssl/ssl_locl.h

ssl/ssl_lib.c

@@ -1116,8 +1116,7 @@ long SSL_ctrl(SSL *s,int cmd,long larg,void *parg)
 			return 0;
 #endif
 
-		if (SSL_version(s) == DTLS1_VERSION ||
-		    SSL_version(s) == DTLS1_BAD_VER)
+		if (SSL_IS_DTLS(s))
 			{
 			s->d1->mtu = larg;
 			return larg;