net-online: only process symbolic links in /sys/class/net
net-online: only process symbolic links in /sys/class/net

The /sys/class/net directory contains files which are not symlinks if
the system has bonded devices [1].  We should ignore these files.

This fixes #196.

[1] https://elkano.org/blog/manage-interface-bondings-sysfs-interface/

williamh/openrc,OpenRC/openrc,williamh/openrc,dwfreed/openrc,williamh/openrc,dwfreed/openrc,dwfreed/openrc,OpenRC/openrc,OpenRC/openrc