Rework the MSI-X and queue-count handling to use the standard iflib
interrupt model and to keep every ring serviced.

• Cap isc_n{tx,rx}qsets_max at the RSS indirection-table size (HW_ATL_RSS_INDIRECTION_QUEUES_MAX, 8) instead of HW_ATL_B0_RINGS_MAX. RSS only steers RX traffic to eight rings, so on hosts with more CPUs the surplus TX rings never make progress: iflib flowid-steers TCP flows across every TX ring, and a flow landing on a surplus ring has its segments queued but never transmitted, hanging the connection.

• Add a TX-specific ifdi_tx_queue_intr_enable that reads tx_rings[txqid]->msix. It was wired to the RX handler, which indexes rx_rings[] with the qid; safe only while tx_rings_count == rx_rings_count, otherwise the lookup walks past rx_rings[] and feeds a garbage msix value into the IRQ mask register.

• Fix three MSI-X / admin-IRQ bugs: the TX softirq was attached to rx_rings[i]->irq (overwriting the RX handle and leaving the TX handle uninitialized); the admin-IRQ failure path dereferenced rx_rings[rx_rings_count], one past the end; and aq_linkstat_isr cleared the admin interrupt by writing the raw vector number instead of BIT(vector).

• Allocate one IFLIB_INTR_RXTX vector per RX/TX queue pair like every other in-tree iflib driver (em/ix/igc, vmxnet3) instead of an IFLIB_INTR_RX vector per RX ring plus a hand-wrapped IFLIB_INTR_TX softirq per TX ring. iflib's iflib_fast_intr_rxtx() then services TX completions on the shared vector through isc_txd_credits_update().