Notice that immediately before the block you quite there is another block:
#
# For now, we do not use the /etc/network/if-{up,down}.d
# stuff yet. Not sure if it is useful for NIS or how
# it should work, exactly.
#
return 0
which ensures that the check for network interfaces is never actually performed. This is true in the upstream Debian package and in version 3.16-1ubuntu3 which appears to be the latest in Ubuntu. I can't see anything which suggests that it has ever been enabled.
Notice that immediately before the block you quite there is another block:
# if-{up, down}.d
# For now, we do not use the /etc/network/
# stuff yet. Not sure if it is useful for NIS or how
# it should work, exactly.
#
return 0
which ensures that the check for network interfaces is never actually performed. This is true in the upstream Debian package and in version 3.16-1ubuntu3 which appears to be the latest in Ubuntu. I can't see anything which suggests that it has ever been enabled.