tcp_input: remove call to soisconnected() on transition to ESTABLISHED

[glebius]

Summary

This call existed since pre-FreeBSD times, and it is hard to understand
why it was there in the first place. After 6f3caa6d815 it definitely
became necessary and commit message from f1ee30ccd60 confirms that.
Now that 6f3caa6d815 is effectively backed out by XXXXXX, the call doesn't
seem to make any use.

[glebius]

Note: I found out that for RACK/BBR this call is still needed (sometimes). Can't understand why.

[rrs]

So if you are not doing soisconnected() here where does it happen at now?

[glebius]

In D36065#819251, @rrs wrote:

So if you are not doing soisconnected() here where does it happen at now?

Now we call solisten_enqueue(, SS_ISCONNECTED). Previously we called sonewconn(, 0) instead of sonewconn(, SS_ISCONNECTED).

The more I look at accept filtered sockets, the more I think they Peter was right today on the call. Let me finish tests and we will see.

[glebius]

As is breaks accept filters and in current form should be abandoned.