Makefile: Use go tool vet for vetting
Makefile: Use go tool vet for vetting

This speeds up the vetting of gofiles by as much as 2x:

Before:
  $ time make govet
    CHECK vetting all GOFILES...
  vet: cilium/cmd/status.go: cilium/cmd/status.go:48:1: expected declaration, found 'IDENT' myb
  vet: no files checked
  exit status 1
  Makefile:206: recipe for target 'govet' failed
  make: *** [govet] Error 1

  real    0m15.506s
  user    0m10.310s
  sys     0m2.865s

After:
  $ time make govet
    CHECK vetting all GOFILES...
  vet: cilium/cmd/status.go: cilium/cmd/status.go:48:1: expected declaration, found 'IDENT' myb
  Makefile:206: recipe for target 'govet' failed
  make: *** [govet] Error 1

  real    0m6.316s
  user    0m3.231s
  sys     0m1.304s

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@covalent.io>

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