[package] base-files: attempt bring up related wifi devices when calling ifup

[package] base-files: attempt bring up related wifi devices when calling ifup
If a user invoked /sbin/ifup to bring up an interface, the setup used to fail
in case of wireless networks tied to a non-bridged interface definition.
Likewise, the bringup of "lan" in the default configuration will reinitialize
the bridge but do not re-join the wireless network to it, requiring an extra
call to /sbin/wifi (which might not be possible anymore due to a severed link
if connected wirelessly).

The changeset modifies the "ifup" command to search for related wireless
devices and call "wifi up" on them if applicable. This way the commands for
wireless and non-wireless interfaces are unified from a cli point of view.

The "ifup -a" case has not been changed to keep the logic of the
/etc/init.d/network boot sequence. This might be changed later.

Solves #9763.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@27720 3c298f89-4303-0410-b956-a3cf2f4a3e73