kernel: smc91x: fix broken irq-context in PREEMPT_RT

A locking context bug was found in the Linux kernel's smc91x Ethernet driver on PREEMPTRT kernels. The smcspecialtrylock function disables IRQs but smcspecialunlock does not properly restore IRQs on PREEMPTRT. This mismatch causes RCU read unlock to fail in devqueuexmit, triggering a "workqueue...