Protocol version selection and negotiation rewrite

The protocol selection code is now consolidated in a few consecutive
short functions in a single file and is table driven.  Protocol-specific
constraints that influence negotiation are moved into the flags
field of the method structure.  The same protocol version constraints
are now applied in all code paths.  It is now much easier to add
new protocol versions without reworking the protocol selection
logic.

In the presence of "holes" in the list of enabled client protocols
we no longer select client protocols below the hole based on a
subset of the constraints and then fail shortly after when it is
found that these don't meet the remaining constraints (suiteb, FIPS,
security level, ...).  Ideally, with the new min/max controls users
will be less likely to create "holes" in the first place.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>

ssl/ssl_conf.c

diff --git a/ssl/ssl_conf.c b/ssl/ssl_conf.c
index 1e14a44..9529d30 100644
--- a/ssl/ssl_conf.c
+++ b/ssl/ssl_conf.c
@@ -347,6 +347,22 @@
     return -1;
 }
 
+static int min_max_proto(SSL_CONF_CTX *cctx, const char *value, int *bound)
+{
+    int method_version;
+    int new_version;
+
+    if (cctx->ctx != NULL)
+        method_version = cctx->ctx->method->version;
+    else if (cctx->ssl != NULL)
+        method_version = cctx->ssl->ctx->method->version;
+    else
+        return 0;
+    if ((new_version = protocol_from_string(value)) < 0)
+        return 0;
+    return ssl_set_version_bound(method_version, new_version, bound);
+}
+
 /*
  * cmd_MinProtocol - Set min protocol version
  * @cctx: config structure to save settings in
@@ -356,13 +372,7 @@
  */
 static int cmd_MinProtocol(SSL_CONF_CTX *cctx, const char *value)
 {
-    int version = protocol_from_string(value);
-
-    if (version < 0)
-        return 0;
-
-    *(cctx->min_version) = version;
-    return 1;
+    return min_max_proto(cctx, value, cctx->min_version);
 }
 
 /*
@@ -374,13 +384,7 @@
  */
 static int cmd_MaxProtocol(SSL_CONF_CTX *cctx, const char *value)
 {
-    int version = protocol_from_string(value);
-
-    if (version < 0)
-        return 0;
-
-    *(cctx->max_version) = version;
-    return 1;
+    return min_max_proto(cctx, value, cctx->max_version);
 }
 
 static int cmd_Options(SSL_CONF_CTX *cctx, const char *value)