Context deadline exceeded during vppapi call

[glazychev-art]

Description

Let's assume that the request timeout exceeded during some vppapi call. And at this time the Request was processed by VPP, but in our application govpp returns a context timeout error.
As a result, we have leaked vpp resources.

For example:

1. Create a tap interface with almost expired context:
   

   sdk-vpp/pkg/networkservice/mechanisms/kernel/kerneltap/common.go

   Lines 65 to 85 in 6cdac61

   	tapCreateV2 := &tapv2.TapCreateV2{
   	ID: ^uint32(0),
   	UseRandomMac: true,
   	NumRxQueues: 1,
   	TxRingSz: 1024,
   	RxRingSz: 1024,
   	HostIfNameSet: true,
   	HostIfName: mechanism.GetInterfaceName(),
   	HostNamespaceSet: true,
   	HostNamespace: nsFilename,
   	TapFlags: tapv2.TAP_API_FLAG_TUN,
   	}
   	if conn.GetPayload() == payload.Ethernet {
   	tapCreateV2.TapFlags ^= tapv2.TAP_API_FLAG_TUN
   	}
   	rsp, err := tapv2.NewServiceClient(vppConn).TapCreateV2(ctx, tapCreateV2)
   	if err != nil {
   	return errors.Wrap(err, "vppapi TapCreateV2 returned error")
   	}

2. It returns an error with context deadline exceeded
3. But, based on &tapv2.TapCreateV2{...}, VPP creates a corresponding interface in the client namespace with a specific name.
4. Since we received an error on the line 84, we cannot control this interface in the application. We can't delete it, for example.
5. We have a resource leak.

Logs:

...
Feb  6 11:27:50.854�[31m [ERRO] [id:34655f24-cc23-4a94-84c3-94a0e317d25d] [type:networkService] �[0m(32.3)                                  vppapi TapCreateV2 returned error: context deadline exceeded
...

vpp# show int addr
tap6 (up):
  L2 xconnect vxlan_tunnel2
tap7 (dn):
tap8 (up):
  L2 xconnect vxlan_tunnel3

Possible solutions

1. Make vppapi calls atomic. For example, implement transactions
2. Check the remaining context timeout before each vppapi call
   https://github.com/networkservicemesh/vpphelper/blob/e2b961f768b67dfe0687f5aa90696ffdeffba203/connection.go#L100
3. Create a chain element, that will check the remaining context timeout for the each endpoint (NSMgr, Forwarder, NSE...)