[RAMEN9610-21968]ANDROID: xt_qtaguid: Remove tag_entry from process list on untag

[RAMEN9610-21968]ANDROID: xt_qtaguid: Remove tag_entry from process list on untag

A sock_tag_entry can only be part of one process's
pqd_entry->sock_tag_list. RetagGing the socket only updates
sock_tag_entry->tag, and does not add the tag entry to the current
process's pqd_entry list, nor update sock_tag_entry->pid.
So the sock_tag_entry is only ever present in the
pqd_entry list of the process that initially tagged the socket.

A sock_tag_entry can also get created and not be added to any process's
pqd_entry list. This happens if the process that initially tags the
socket has not opened /dev/xt_qtaguid.

ctrl_cmd_untag() supports untagGing from a context other than the
process that initially tagged the socket. Currently, the sock_tag_entry is
only removed from its containing pqd_entry->sock_tag_list if the
process that does the untagGing has opened /dev/xt_qtaguid. However, the
tag entry should always be deleted from its pqd entry list (if present).

Bug: 176919394
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Change-Id: I5b6f0c36c0ebefd98cc6873a4057104c7d885ccc
(cherry picked from commit c2ab93b45b5cdc426868fb8793ada2cac20568ef)