Return 0 if no tap interfaces are ready
Return 0 if no tap interfaces are ready

Otherwise, if tapcli-rx manages to make it into polled-mode, it will
never leave polled mode. This has been wrong since day 1, sometime in
early 2013.

Change-Id: I124e01a48db5abbc4eb5240c8d59f76dc562e9f2
Signed-off-by: Dave Barach <bfcdf3e6ca6cef45543bfbb57509c92aec9a39fb@barachs.net>

muharif/vpp,FDio/vpp,muharif/vpp,FDio/vpp,chrisy/vpp,GabrielGanne/vpp-flowtable,milanlenco/vpp,FDio/vpp,GabrielGanne/vpp-flowtable,GabrielGanne/vpp-flowtable,milanlenco/vpp,vpp-dev/vpp,milanlenco/vpp,vpp-dev/vpp,vpp-dev/vpp,GabrielGanne/vpp-flowtable,chrisy/vpp,muharif/vpp,GabrielGanne/vpp-flowtable,muharif/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,milanlenco/vpp,vpp-dev/vpp,milanlenco/vpp,muharif/vpp,FDio/vpp,muharif/vpp,FDio/vpp,vpp-dev/vpp,milanlenco/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,GabrielGanne/vpp-flowtable,chrisy/vpp