Set SO_KEEPALIVE on client sockets if configured to do so.

src/redis.c

@@ -1130,6 +1130,7 @@ void initServerConfig() {
     server.dbnum = REDIS_DEFAULT_DBNUM;
     server.verbosity = REDIS_NOTICE;
     server.maxidletime = REDIS_MAXIDLETIME;
+    server.tcpkeepalive = 0;
     server.client_max_querybuf_len = REDIS_MAX_QUERYBUF_LEN;
     server.saveparams = NULL;
     server.loading = 0;