gnrc_tcp leaks memory when gnrc_netapi_send fails

[nmeum]

gnrc_tcp uses gnrc_netapi_send in two places:

RIOT/sys/net/gnrc/transport_layer/tcp/gnrc_tcp_eventloop.c

Line 221 in 20dec77

gnrc_netapi_send(gnrc_tcp_pid, reset);

RIOT/sys/net/gnrc/transport_layer/tcp/gnrc_tcp_pkt.c

Line 274 in 45989aa

gnrc_netapi_send(gnrc_tcp_pid, out_pkt);

Unfortunately, the return value isn't checked and it seems to me that the caller is responsible for freeing the pktbuf memory on error. As an example: Consider how gnrc_ipv6 handles this:

RIOT/sys/net/gnrc/network_layer/ipv6/gnrc_ipv6.c

Lines 262 to 265 in 7f2cc4f

	if (gnrc_netapi_send(netif->pid, pkt) < 1) {
	DEBUG("ipv6: unable to send packet\n");
	gnrc_pktbuf_release(pkt);
	}

This shouldn't be a big issue as gnrc_netapi_send only fails when msg_try_send fails this is just a minor issue I noticed while debugging #12001.

[brummer-simon]

I'll look into it on the Weekend.