Add more verbose logging during DH key exchange.

The event log messages generated during DH key exchange now include both the
modulus size and hash algorithm used as well as whether the DH parameters
are from one of the standardized groups or were supplied by the server
during Group Exchange.

sshdh.c

@@ -209,6 +209,14 @@ struct dh_ctx *dh_setup_gex(Bignum pval, Bignum gval)
     return ctx;
 }
 
+/*
+ * Return size of DH modulus p.
+ */
+int dh_modulus_bit_size(const struct dh_ctx *ctx)
+{
+    return bignum_bitcount(ctx->p);
+}
+
 /*
  * Clean up and free a context.
  */