bridge-utils: add upstream patch fixing sysfs writes

Add upstream patch that fixes a sysfs path in br_set.
The patch is on top of the latest release 1.5, which already dates from
2011.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>