interface: allow an interface's index to be given in 'sh int'
interface: allow an interface's index to be given in 'sh int'

Type: improvement

e.g.:
DBGvpp# sh int 3
              Name               Idx    State  MTU (L3/IP4/IP6/MPLS)     Counter          Count
loop2                             3     down         9000/0/0/0

Signed-off-by: Neale Ranns <c8ca090d26e35fc94cb9c8fe2fb2efcfa843d561@graphiant.com>
Change-Id: Ie296167ab2b1b9576b46f6d4d9fb9546aef3a0da

chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp