Trim skb linear data

Temporary fix for case when headers starts in skblinear data

Fixed pointer to frame header for 304 response

Author: const-t

fw/cache.c

@@ -849,6 +849,8 @@ tfw_cache_send_304(TfwHttpReq *req, TfwCacheEntry *ce)
 		r = tfw_h2_resp_status_write(resp, 304, false, true);
 		if (unlikely(r))
 			goto err_setup;
+
+		resp->mit.frame_head = it->skb_head->data;
 	}
 
 	/* Put 304 headers */

fw/http_msg.c

@@ -1517,7 +1517,8 @@ tfw_h2_msg_cutoff_headers(TfwHttpResp *resp, TfwHttpRespCleanup* cleanup)
 
 			if ((begin <= off) && (end >= off)) {
 				it->frag = -1;
-				/* TODO: Handle this case, most likely for low MTU*/
+				/* TODO: Handle this case, most likely for low MTU
+				 * it will be implemented as part of #1703 */
 				return;
 			}
 		}
@@ -1566,6 +1567,10 @@ tfw_h2_msg_cutoff_headers(TfwHttpResp *resp, TfwHttpRespCleanup* cleanup)
 			(si->nr_frags) * sizeof(skb_frag_t));
 	}
 
+	/* Trim skb linear data. This is ugly hotfix and must be removed after
+	 * implementation of #1703 */
+	it->skb->len -= skb_headlen(it->skb);
+
 	it->skb_head = it->skb;
 	resp->msg.skb_head = it->skb;