svcrdma: Reject Read lists that exceed the page budget

In the Linux kernel, the following vulnerability has been resolved: svcrdma: Reject Read lists that exceed the page budget Individual Read segment lengths are validated at decode time, but nothing prevents a requester from sending multiple segments whose cumulative length exceeds the rq_pages array budget. When one segment fills the page array exactly, the runtime guard in svc_rdma_build_read_segment() is bypassed because len reaches zero. A subsequent segment then accesses the NULL sentinel slot at rq_pages[rq_maxpages], resulting in a NULL pointer dereference during DMA mapping. Accumulate pages across all Read segments and reject the message at decode time when the total would overflow the page budget.