Fix integer overflow in OpenFlow meter stats

[Av1ralS1ngh]

GetMeterStats retrieves per-meter packet drop counts from OVS via OpenFlow multipart replies. The OVS PacketBandCount field isuint64, but the callback signature truncated it to int64, causing silent overflow when cumulative drop counts exceed math.MaxInt64.

This change updates the entire call chain to use uint64:

What changed:

• pkg/ovs/openflow/interfaces.go: updated GetMeterStats callback signature from func(int, int64) to func(int, uint64).

• pkg/ovs/openflow/ofctrl_bridge.go: removed explicit int64 cast; stats.BandStats[0].PacketBandCount is passed directly as uint64.

• pkg/agent/openflow/client.go: updated handleMeterStatsReply to accept uint64.

• pkg/agent/openflow/pipeline.go: changed ovsMeterPacketDrops from map[int]*atomic.Int64 to map[int]*atomic.Uint64.

• pkg/ovs/openflow/ofctrl_bridge_test.go: aligned test assertions with uint64 types.

• pkg/ovs/openflow/testing/mock_openflow.go: regenerated mock to match updated interface.

• pkg/agent/openflow/meter_test.go [NEW]: test covering initial counts, incremental updates, and values exceeding MaxInt64.

  Fixes Integer overflow in OpenFlow meter stats handling #7784