base-files: fix backwards compatiblity of rc.common EXTRA_COMMANDS

base-files: fix backwards compatiblity of rc.common EXTRA_COMMANDS

Avoid needlessly breaking old initscripts that set EXTRA_COMMANDS. This
will aid in debugging (as it simplifies reverting to an older version of
a package) and unbreaks third-party feeds (and packages that maintain
their OpenWrt initscripts as part of the software's repo instead of the
OpenWrt feed like fastd).

Without this, initscripts that set EXTRA_COMMANDS become completely
unusable, as all default commands like start/stop cease working.

Fixes: 1a69f50dc627 ("base-files: fix rc.common help alignment")
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>