Improve comment about why we disable TLS compression.

Closes bug 22964.  Based on Teor's replacement there, but tries
to put the comment in a more logical place, and explain why we're
actually disabling compression in the first place.

src/common/tortls.c

@@ -1174,17 +1174,20 @@ tor_tls_context_new(crypto_pk_t *identity, unsigned int key_lifetime,
     SSL_CTX_set_options(result->ctx,
                         SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION);
   }
+
+  /* Don't actually allow compression; it uses RAM and time, it makes TLS
+   * vulnerable to CRIME-style attacks, and most of the data we transmit over
+   * TLS is encrypted (and therefore uncompressible) anyway. */
 #ifdef SSL_OP_NO_COMPRESSION
   SSL_CTX_set_options(result->ctx, SSL_OP_NO_COMPRESSION);
 #endif
 #if OPENSSL_VERSION_NUMBER < OPENSSL_V_SERIES(1,1,0)
 #ifndef OPENSSL_NO_COMP
-  /* Don't actually allow compression; it uses ram and time, but the data
-   * we transmit is all encrypted anyway. */
   if (result->ctx->comp_methods)
     result->ctx->comp_methods = NULL;
 #endif
 #endif
+
 #ifdef SSL_MODE_RELEASE_BUFFERS
   SSL_CTX_set_mode(result->ctx, SSL_MODE_RELEASE_BUFFERS);
 #endif