Slugs are not customizable when BP is network activated and the BP root blog is not main site

[imath]

On multisite configs, having BuddyPress activated on the network and its root blog set to a subsite is a config I forgot to test (my bad 😔). I just tested it since an issue about slugs was raised in support forums by @perchenet.

See: ​https://buddypress.org/support/topic/buddypress-12-0-0/page/5/#post-332447

When upgrading from 11.4.0 to 12.0.0, the migration task is rightly performed: BuddyPress pages are migrated as buddypress post type and it happens into the $subsite corresponding to define( 'BP_ROOT_BLOG', $subsite ).

But as soon as I want to customize slugs from the URLs tab of the Network BuddyPress settings, changes are not saved.

Tasks:

• Fix the above issue,
• Check the tool to reset slugs
• Simulate another upgrade having pages named like BuddyPress directories on the main site (this is to check the initial -3 post name suffix bug raised by @perchenet.

• [x] Fixes the customization issue,
• [x] Checked the tool to reset slugs
• [x] Simulated another upgrade having pages named like directories on the main site and no slug conflicts were found (no $suffix were added to buddypress post types slugs.

Trac ticket: ​https://buddypress.trac.wordpress.org/ticket/9048

I've also tested this PR successfully for regular BuddyPress installs:

• non multisite
• multisite network activated
• multisite activated on a subsite.

[imath]

In 13678:

Make sure slugs are customizable for the BP root site

On multisite configs the BP root site can be different than the current WordPress site. It's necessary to eventually switch to the BP root site before saving custom slugs or retrieving them.

Props perchenet

See #9048 (trunk)
Closes ​https://github.com/buddypress/buddypress/pull/206

[imath]

In 13679:

Make sure slugs are customizable for the BP root site

On multisite configs the BP root site can be different than the current WordPress site. It's necessary to eventually switch to the BP root site before saving custom slugs or retrieving them.

Props perchenet

Fixes #9048 (branch 12.0)