RDMA/rxe: Fix TOCTOU heap overflow in get_srq_wqe

In the Linux kernel, the following vulnerability has been resolved: RDMA/rxe: Fix TOCTOU heap overflow in get_srq_wqe get_srq_wqe() reads wqe->dma.num_sge from the shared receive queue buffer, which is mapped into userspace. It validates num_sge against max_sge, but then re-reads the same field to calculate the memcpy size. A concurrent userspace thread can modify num_sge between validation and use, causing a heap buffer overflow when copying the WQE into qp->resp.srq_wqe. Read num_sge into a local variable and use it for both the bounds check and the size calculation.