All sys-apps/openrc ebuilds as of today do explicitly set the permissions of /etc/netif.d to 0644, using this statement:

chmod -R 0644 ${D}/etc/netif.d || die

I suppose the intention is to change permissions of the contained files to the given value, but apparently this applies to the directory as well. Of course, this is wrong since directories need to be executable.

Assuming there might be subdirectories to /etc/netif.d in the future, a possible fix would be to:
bg. find /etc/netif.d -type f -exec chmod 0644 '{}' \; -o -type d -exec chmod 0755 '{}' \;