Staging: hv: rename ChannelInterface.c and .h to channel_interface.c and .h

All of the uppercase .c files are now gone.

Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>