Add missing dtrace receive and send probes for TCP

[tuexen]

Summary

TCP was missing a couple of send and receive probes for dtrace, mostly in the syn-cache handling and the handling of the TIMEWAIT state. This patch fixes that.

Test Plan

Execute the tests from D16288.

[markj]

sys/netinet/tcp_timewait.c

458 ↗

(On Diff #45626)

I would use an "else" here instead of adding an extra label and goto.

[tuexen]

sys/netinet/tcp_timewait.c

458 ↗

(On Diff #45626)

So you would prefer:

	/*
	 * Acknowledge the segment if it has data or is not a duplicate ACK.
	 */
	if (thflags != TH_ACK || tlen != 0 ||
	    th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt) {
		TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
		tcp_twrespond(tw, TH_ACK);
	} else {
drop:
		TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
	}
	INP_WUNLOCK(inp);
	m_freem(m);
	return (0);
}

I thought about it, but didn't like the drop label inside an else clause...
Do you really prefer it? If yes, I'll change. Please let me know.

[markj]

sys/netinet/tcp_timewait.c

458 ↗

(On Diff #45626)

I don't prefer it strongly enough to insist upon it, especially since I don't work on TCP. :) The version here is fine with me.

[rrs]

sys/netinet/tcp_timewait.c

458 ↗

(On Diff #45626)

I like it with the label. The drop inside the else is not something
I would like to see.