Tap plugin

This PR adds a plugin to create tap devices.
The plugin adds a tap device to the container.

The plugin has a workaround for a golang netlink library
which does not allow for tap devices with no owner/group
to be created. When no tap owner/group is requested, the
plugin will fall back to using the ip tool for creating
the tap device. A fix to the golang netlink lib is pending.

Signed-off-by: mmirecki <mmirecki@redhat.com>

vendor/github.com/opencontainers/selinux/pkg/pwalk/README.md

@@ -0,0 +1,42 @@
+## pwalk: parallel implementation of filepath.Walk
+
+This is a wrapper for [filepath.Walk](https://pkg.go.dev/path/filepath?tab=doc#Walk)
+which may speed it up by calling multiple callback functions (WalkFunc) in parallel,
+utilizing goroutines.
+
+By default, it utilizes 2\*runtime.NumCPU() goroutines for callbacks.
+This can be changed by using WalkN function which has the additional
+parameter, specifying the number of goroutines (concurrency).
+
+### Caveats
+
+Please note the following limitations of this code:
+
+* Unlike filepath.Walk, the order of calls is non-deterministic;
+
+* Only primitive error handling is supported:
+
+  * filepath.SkipDir is not supported;
+
+  * no errors are ever passed to WalkFunc;
+
+  * once any error is returned from any WalkFunc instance, no more new calls
+    to WalkFunc are made, and the error is returned to the caller of Walk;
+
+  * if more than one walkFunc instance will return an error, only one
+    of such errors will be propagated and returned by Walk, others
+    will be silently discarded.
+
+### Documentation
+
+For the official documentation, see
+https://pkg.go.dev/github.com/opencontainers/selinux/pkg/pwalk?tab=doc
+
+### Benchmarks
+
+For a WalkFunc that consists solely of the return statement, this
+implementation is about 10% slower than the standard library's
+filepath.Walk.
+
+Otherwise (if a WalkFunc is doing something) this is usually faster,
+except when the WalkN(..., 1) is used.