feat: implement Port and Mempool initialization with comprehensive tests

[gspivey]

Summary

• Port management (dpdk/src/port.rs): Full implementation of DPDK port initialization, configuration, and packet I/O operations including PortConfig, MacAddress, LinkStatus, PortStats, and burst-based RX/TX
• Mempool management (dpdk/src/mbuf.rs): Complete mempool creation with MempoolConfig builder pattern, bulk allocation, and pool status queries
• Enhanced stubs (dpdk-sys/src/stubs.rs): Working stub implementations that return valid pointers for testing

Test plan

• All 48 unit tests in dpdk crate pass (17 for Port, 28 for Mempool, 3 existing)
• All 3 unit tests in dpdk-sys crate pass
• All 8 unit tests in dpdk-tokio crate pass
• cargo build succeeds
• cargo test passes (59 total tests)

Add real implementations for DPDK port and mempool management:

Port (dpdk/src/port.rs):

• PortConfig with queue count, descriptor counts, promiscuous mode, MTU
• MacAddress with utility methods (is_broadcast, is_multicast, is_zero)
• LinkStatus and PortStats types
• Port::init() with device info validation and queue setup
• Port::start/stop with promiscuous mode support
• rx_burst/tx_burst for packet I/O
• 17 unit tests

Mempool (dpdk/src/mbuf.rs):

• MempoolConfig builder pattern
• Mempool::create() calling rte_pktmbuf_pool_create
• Mempool::create_with_config() and create_default() helpers
• alloc_bulk() for batch allocation
• available_count(), in_use_count(), is_full(), is_empty()
• 28 unit tests

Error types (dpdk/src/error.rs):

• MempoolCreateFailed, QueueSetupFailed, InvalidName variants

Stubs (dpdk-sys/src/stubs.rs):

• SOCKET_ID_ANY constant
• rte_mempool struct with size/populated_size fields
• rte_pktmbuf_pool_create returns valid mempool
• rte_pktmbuf_alloc/alloc_bulk return valid mbufs with buffers
• rte_mempool_avail_count, in_use_count, full, empty functions

https://claude.ai/code/session_01UiHnsVmMyk1CJgck3cCYZQ