xprtrdma: Store RDMA credits in unsigned variables
Dan Carpenter's static checker pointed out:
net/sunrpc/xprtrdma/rpc_rdma.c:879 rpcrdma_reply_handler()
warn: can 'credits' be negative?
"credits" is defined as an int. The credits value comes from the
server as a 32-bit unsigned integer.
A malicious or broken server can plant a large unsigned integer in
that field which would result in an underflow in the following
logic, potentially triggering a deadlock of the mount point by
blocking the client from issuing more RPC requests.