Fix formation walking following "improved ship pickup"/rP23925

Summary:
As reported by @bb and @Angen , rP23925 broke formation walking in a few situations.

The issue is that rP23867/D2871 requires formation members to get no messages until the controller is stopped, but rP23925 didn't use the correct function (on account of a missed rebase), so members stopped too early.

Reported by: bb, Angen

Reviewed By: bb

Differential Revision: https://code.wildfiregames.com/D3006