RDMA/hfi1: Fix potential integer multiplication overflow errors

In the Linux kernel, the following vulnerability has been resolved: RDMA/hfi1: Fix potential integer multiplication overflow errors When multiplying of different types, an overflow is possible even when storing the result in a larger type. This is because the conversion is done after the multiplication. So arithmetic overflow and thus in incorrect value is possible. Correct an instance of this in the inter packet delay calculation. Fix by ensuring one of the operands is u64 which will promote the other to u64 as well ensuring no overflow.