Staging: hv: netvsc_drv: Make the function rndis_filter_send() non-static

In preparation to getting rid of struct netvsc_driver,
make the function  rndis_filter_send()  non-static.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Abhishek Kane <v-abkane@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>