use libnetwork/slirp4netns from c/common

Most of the code moved there so if from there and remove it here.

Some extra changes are required here. This is a bit of a mess. The pipe
handling makes this a bit more difficult.

[NO NEW TESTS NEEDED] This is just a rework, existing tests must pass.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

vendor/github.com/containers/common/pkg/rootlessport/rootlessport_linux.go

@@ -0,0 +1,27 @@
+//go:build linux
+// +build linux
+
+// Rootlessport Config type for use in podman/cmd/rootlessport.
+package rootlessport
+
+import (
+	"github.com/containers/common/libnetwork/types"
+)
+
+const (
+	// BinaryName is the binary name for the parent process.
+	BinaryName = "rootlessport"
+)
+
+// Config needs to be provided to the process via stdin as a JSON string.
+// stdin needs to be closed after the message has been written.
+type Config struct {
+	Mappings    []types.PortMapping
+	NetNSPath   string
+	ExitFD      int
+	ReadyFD     int
+	TmpDir      string
+	ChildIP     string
+	ContainerID string
+	RootlessCNI bool
+}