res_pjsip: Set TCP_NODELAY on TCP transports

Although it's perfectly legal to place multiple SIP messages in the same packet,
it can cause problems because the Linux default is to enable Path MTU Discovery
which sets the Don't Fragment bit on the packets. If adding a second message to
the packet causes the MTU to be exceeded, and the destination isn't equipped to
send a FRAGMENTATION NEEDED response to a large packet, the packet will just be
dropped.

We can't specifically tell the stack to send only 1 message per packet, but we
can turn on TCP_NODELAY when we create the transport. This will at least tell
the stack to send packets as soon as possible.

ASTERISK-26005 #close
Reported-by: Ross Beer

Change-Id: I820f23227183f2416ca5e393bec510e8fe1c8fbd

res/res_pjsip/config_transport.c

@@ -562,11 +562,17 @@ static int transport_apply(const struct ast_sorcery *sorcery, void *obj)
 		}
 	} else if (transport->type == AST_TRANSPORT_TCP) {
 		pjsip_tcp_transport_cfg cfg;
+		int option = 1;
 
 		pjsip_tcp_transport_cfg_default(&cfg, temp_state->state->host.addr.sa_family);
 		cfg.bind_addr = temp_state->state->host;
 		cfg.async_cnt = transport->async_operations;
 		set_qos(transport, &cfg.qos_params);
+		cfg.sockopt_params.options[0].level = pj_SOL_TCP();
+		cfg.sockopt_params.options[0].optname = pj_TCP_NODELAY();
+		cfg.sockopt_params.options[0].optval = &option;
+		cfg.sockopt_params.options[0].optlen = sizeof(option);
+		cfg.sockopt_params.cnt = 1;
 
 		for (i = 0; i < BIND_TRIES && res != PJ_SUCCESS; i++) {
 			if (perm_state && perm_state->state && perm_state->state->factory