intra/ipn: turn off TCP keepalive by default

[Lanius-collaris]

Closes #144

[ignoramous]

Thanks.

This change could be made in rwext instead and a call to core.SetKeepAliveConfSockOpt be removed from all other places (like auto.go)?

rwext will also have to set the kacfg for DialerOpts.LowerKeepAlive now.

firestack/intra/rwconn.go

Lines 29 to 38 in 4035893

	func (rw rwext) SetAsTCPSockOpt() (c *net.TCPConn, ok bool) {
	r, w := rw.deadlines()
	timeout := max(int(r), int(w))
	c, ok = rw.Conn.(*net.TCPConn) // no-op for tcp conns
	if ok && r > 0 {
	// always returns false for udp conns
	ok = core.SetTimeoutSockOpt(c, timeout*1000)
	}
	return c, ok
	}