hyperv: fix sparse warnings

this patch fixes following sparse warnings:

netvsc.c:688:5: warning: symbol 'netvsc_copy_to_send_buf' was not declared. Should it be static?
rndis_filter.c:627:5: warning: symbol 'rndis_filter_set_offload_params' was not declared. Should it be static?
rndis_filter.c:702:5: warning: symbol 'rndis_filter_set_rss_param' was not declared. Should it be static?

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>