Extract priv_validator into first class package

This is a maintenance change to move the private validator package out
of the types and to a top-level location. There is no good reason to
keep it under the types and it will more clearly coommunicate where
additions related to the privval belong. It leaves the interface and the
mock in types for now as it would introduce circular dependency between
privval and types, this should be resolved eventually.

* mv priv_validator to privval pkg
* use consistent `privval` as import

Follow-up to #1255

privval/socket_tcp.go

@@ -0,0 +1,66 @@
+package privval
+
+import (
+	"net"
+	"time"
+)
+
+// timeoutError can be used to check if an error returned from the netp package
+// was due to a timeout.
+type timeoutError interface {
+	Timeout() bool
+}
+
+// tcpTimeoutListener implements net.Listener.
+var _ net.Listener = (*tcpTimeoutListener)(nil)
+
+// tcpTimeoutListener wraps a *net.TCPListener to standardise protocol timeouts
+// and potentially other tuning parameters.
+type tcpTimeoutListener struct {
+	*net.TCPListener
+
+	acceptDeadline time.Duration
+	connDeadline   time.Duration
+	period         time.Duration
+}
+
+// newTCPTimeoutListener returns an instance of tcpTimeoutListener.
+func newTCPTimeoutListener(
+	ln net.Listener,
+	acceptDeadline, connDeadline time.Duration,
+	period time.Duration,
+) tcpTimeoutListener {
+	return tcpTimeoutListener{
+		TCPListener:    ln.(*net.TCPListener),
+		acceptDeadline: acceptDeadline,
+		connDeadline:   connDeadline,
+		period:         period,
+	}
+}
+
+// Accept implements net.Listener.
+func (ln tcpTimeoutListener) Accept() (net.Conn, error) {
+	err := ln.SetDeadline(time.Now().Add(ln.acceptDeadline))
+	if err != nil {
+		return nil, err
+	}
+
+	tc, err := ln.AcceptTCP()
+	if err != nil {
+		return nil, err
+	}
+
+	if err := tc.SetDeadline(time.Now().Add(ln.connDeadline)); err != nil {
+		return nil, err
+	}
+
+	if err := tc.SetKeepAlive(true); err != nil {
+		return nil, err
+	}
+
+	if err := tc.SetKeepAlivePeriod(ln.period); err != nil {
+		return nil, err
+	}
+
+	return tc, nil
+}