[Calico/VPP NSM integration] memif and memifproxy files should be shared with VPP pod

[Bolodya1997]

Issue

Currently memif and memifproxy uses /tmp/memif and /tmp/memifproxy directories for storing socket files. VPP pod has no access to these files, so it work with them.

sdk-vpp/pkg/networkservice/mechanisms/memif/common.go

Lines 199 to 201 in 7e89964

	func socketFile(conn *networkservice.Connection) string {
	return filepath.Join(os.TempDir(), "memif", conn.GetId(), "memif.socket")
	}

sdk-vpp/pkg/networkservice/mechanisms/memif/memifproxy/client.go

Lines 82 to 84 in 7e89964

	func listenSocketFilename(conn *networkservice.Connection) string {
	return filepath.Join(os.TempDir(), "memifproxy", conn.GetId(), "memif.socket")
	}

Parent issue

networkservicemesh/integration-k8s-kind#325

Possible solution

Use shared directory

We can use /var/run/vpp directory instead of /tmp as a base for creating directories for memif socket files.

Use /proc/x/fd/y path

We can replace common /tmp/... path with /proc/x/fd/y path before making VPP API request - such path is already shared, but it will additionally force us to use hostPid: true for the Client applications.
Currently VPP is responsible for creating memif sockets - we are only providing the path where they should be located. With this solution we need to perform additional actions for creating memif socket by ourselves before requesting VPP.

[Bolodya1997]

@edwarnicke @denis-tingaikin
cc

[Bolodya1997]

Possible solution with using abstract sockets - https://gerrit.fd.io/r/c/vpp/+/32271/6/src/plugins/memif/memif.api#43.

[Bolodya1997]

Should be closed with #370

[denis-tingaikin]

It seems like all PRs have merged.