CVE-2026-72495: RDMA/bnxt_re: Avoid repeated requests to allocate WC pages

In the Linux kernel, the following vulnerability has been resolved:

RDMA/bnxtre: Avoid repeated requests to allocate WC pages

Applications can request multiple WC pages for the same ucontext. As of now, only 1 WC page per ucontext is supported. Add a lock to avoid concurrent access and a check to fail repeated requests. Also, if the mmap entry insert fails for the WC, free the Doorbell page index mapped for the WC page.