Use sbuf_drain unconditionally

After making sbuf_drain safe for external use,
there is no need to protect the call.

MFC after: 2 weeks
Reviewed By: tuexen, #transport
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D29545

sys/netinet/tcp_hostcache.c

@@ -644,7 +644,6 @@ sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
 	const int linesize = 128;
 	struct sbuf sb;
 	int i, error, len;
-	bool do_drain = false;
 	struct hc_metrics *hc_entry;
 	char ip4buf[INET_ADDRSTRLEN];
 #ifdef INET6
@@ -702,15 +701,9 @@ sysctl_tcp_hc_list(SYSCTL_HANDLER_ARGS)
 			    hc_entry->rmx_hits,
 			    hc_entry->rmx_updates,
 			    hc_entry->rmx_expire);
-			do_drain = true;
 		}
 		THC_UNLOCK(&V_tcp_hostcache.hashbase[i].hch_mtx);
-		/* Need to track if sbuf has data, to avoid
-		 * a KASSERT when calling sbuf_drain.
-		 */
-		if (do_drain) {
-			sbuf_drain(&sb);
-			do_drain = false;
+		sbuf_drain(&sb);
 		}
 	}
 #undef msec