Staging: hv: netvsc: Cleanup the name and type of link_stat variable

Consistently name the variable tracking the link status. Use a consistent
type for this variable and get rid of some unnecessary parentheses as well.
I would like to thank Joe Perches <joe@perches.com> for suggesting these
changes and patiently helping me get here!

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>