Add the vendor hook to user.c, because of some speical cases related to
our feature, we need to initialize the variables defined by ourselves in
user_struct, so we add the hook at alloc_uid to make sure we can go to
our own logic when the user_struct is about to initialize.
Bug: 187458531
Signed-off-by: heshuai1 <heshuai1@xiaomi.com>
Change-Id: I078484aac2c3d396aba5971d6d0f491652f3781c
