liquidio: move a couple of functions to lio_core.c

To support the next patch in this series which has code that calls
octnet_get_link_stats from two different .c files, move that function (and
its dependency octnet_nic_stats_callback) to lio_core.c.  Remove
octnet_get_link_stats's static declaration and add its function prototype
in octeon_network.h.

Signed-off-by: Pradeep Nalla <pradeep.nalla@cavium.com>
Acked-by: Raghu Vatsavayi <raghu.vatsavayi@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>