octeontx2-pf: fix a buffer overflow in otx2_set_rxfh_context()

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

octeontx2-pf: fix a buffer overflow in otx2_set_rxfh_context()

This function is called from ethtool_set_rxfh() and "*rss_context" comes from the user. Add some bounds checking to prevent memory corruption.