linux: netfront: Fix grant that wasnt mapped
linux: netfront: Update to netmap API 11

nm_txsync/nm_rxsync now receives a netmap_kring directly instead
of an netmap_adapter.
linux: netback: Update to netmap API 11

nm_txsync/nm_rxsync now receives a netmap_kring directly instead
of an netmap_adapter.
netmap: Update submodule to API 11