Python/ifconfig: T1557: migrate all sysfs calls to {read,write}_sysfs helper
Python/ifconfig: T1557: migrate all sysfs calls to {read,write}_sysfs helper

Introduced in commit f524254 ("Python/ifconfig: T1557: use read/write helpers
to interface with sysfs") migrate all remaining calls to this new helper.

This enables us to have a single debug call and a single place for error
checking.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x