liquidio: declare liquidio_set_rxcsum_command static

liquidio_set_rxcsum_command is a local function only, no need to expose
it outside of lio_main.c so declare it static and make sparse happy.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>