eni: Fix data race around Node.k8sObj
eni: Fix data race around Node.k8sObj

This fixes a data race found when running the unit-tests with `-race`.

```
WARNING: DATA RACE
Write at 0x00c000067168 by goroutine 118:
  github.com/cilium/cilium/pkg/aws/eni.(*Node).UpdatedNode()
      /home/chris/code/cilium/cilium/pkg/aws/eni/node.go:69 +0x5f
  github.com/cilium/cilium/pkg/ipam.(*Node).UpdatedResource()
      /home/chris/code/cilium/cilium/pkg/ipam/node.go:319 +0x81
  github.com/cilium/cilium/pkg/ipam.(*NodeManager).Update()
      /home/chris/code/cilium/cilium/pkg/ipam/node_manager.go:273 +0x14a
  github.com/cilium/cilium/pkg/aws/eni.(*ENISuite).TestNodeManagerReleaseAddress()
      /home/chris/code/cilium/cilium/pkg/aws/eni/node_manager_test.go:467 +0x101d
  runtime.call32()
      /usr/lib/go/src/runtime/asm_amd64.s:539 +0x3a
  reflect.Value.Call()
      /usr/lib/go/src/reflect/value.go:321 +0xd3
  gopkg.in/check%2ev1.(*suiteRunner).forkTest.func1()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/check.go:781 +0xa0a
  gopkg.in/check%2ev1.(*suiteRunner).forkCall.func1()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/check.go:675 +0xd9

Previous read at 0x00c000067168 by goroutine 324:
  github.com/cilium/cilium/pkg/aws/eni.(*Node).getLimits()
      /home/chris/code/cilium/cilium/pkg/aws/eni/node.go:101 +0x5a
  github.com/cilium/cilium/pkg/aws/eni.(*Node).GetMaximumAllocatableIPv4()
      /home/chris/code/cilium/cilium/pkg/aws/eni/node.go:488 +0x2e2
  github.com/cilium/cilium/pkg/ipam.(*Node).getMaxAllocate()
      /home/chris/code/cilium/cilium/pkg/ipam/node.go:213 +0x79
  github.com/cilium/cilium/pkg/ipam.(*Node).recalculate()
      /home/chris/code/cilium/cilium/pkg/ipam/node.go:368 +0x42a
  github.com/cilium/cilium/pkg/ipam.(*NodeManager).resyncNode()
      /home/chris/code/cilium/cilium/pkg/ipam/node_manager.go:342 +0x7a
  github.com/cilium/cilium/pkg/ipam.(*NodeManager).Resync.func1()
      /home/chris/code/cilium/cilium/pkg/ipam/node_manager.go:389 +0x88

Goroutine 118 (running) created at:
  gopkg.in/check%2ev1.(*suiteRunner).forkCall()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/check.go:672 +0x44d
  gopkg.in/check%2ev1.(*suiteRunner).forkTest()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/check.go:763 +0x1b9
  gopkg.in/check%2ev1.(*suiteRunner).runTest()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/check.go:818 +0x228
  gopkg.in/check%2ev1.(*suiteRunner).run()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/check.go:624 +0x1c7
  gopkg.in/check%2ev1.Run()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/run.go:92 +0x5a
  gopkg.in/check%2ev1.RunAll()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/run.go:84 +0x127
  gopkg.in/check%2ev1.TestingT()
      /home/chris/code/cilium/cilium/vendor/gopkg.in/check.v1/run.go:72 +0x5f6
  github.com/cilium/cilium/pkg/aws/eni.Test()
      /home/chris/code/cilium/cilium/pkg/aws/eni/eni_test.go:26 +0x38
  testing.tRunner()
      /usr/lib/go/src/testing/testing.go:991 +0x1eb

Goroutine 324 (finished) created at:
  github.com/cilium/cilium/pkg/ipam.(*NodeManager).Resync()
      /home/chris/code/cilium/cilium/pkg/ipam/node_manager.go:388 +0x2c5
  github.com/cilium/cilium/pkg/ipam.NewNodeManager.func1()
      /home/chris/code/cilium/cilium/pkg/ipam/node_manager.go:168 +0x101
  github.com/cilium/cilium/pkg/trigger.(*Trigger).waiter()
      /home/chris/code/cilium/cilium/pkg/trigger/trigger.go:206 +0x4b9
```

Signed-off-by: Chris Tarazi <711c73f64afdce07b7e38039a96d2224209e9a6c@isovalent.com>

cilium-team/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,cilium-team/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium