ethtool: fail closed if we can't get max channel used in indirection tables

In the Linux kernel, the following vulnerability has been resolved: ethtool: fail closed if we can't get max channel used in indirection tables Commit 0d1b7d6c9274 ("bnxt: fix crashes when reducing ring count with active RSS contexts") proves that allowing indirection table to contain channels with out of bounds IDs may lead to crashes. Currently the max channel check in the core gets skipped if driver can't fetch the indirection table or when we can't allocate memory. Both of those conditions should be extremely rare but if they do happen we should try to be safe and fail the channel change.