ANDROID: xt_qtaguid: fix UAF race

Make sure to hold the sock_tag_list_lock while accessing the tag to
avoid a race between getting the tag and free'ing the tag.

Bug: 184018316
Fixes: c7ca0ac69702 ("ANDROID: netfilter: xt_qtaguid: add qtaguid matching module")
Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: Ia44dfcc1693bc3de1d767e024d09c11f4a8b02f9
Git-commit: 2398e650c58a6f4877dafce649188290f6e3b4f5
Git-repo: https://android.googlesource.com/kernel/msm


Signed-off-by: PavanKumar S.R. <pavasr@codeaurora.org>