ANDROID: roll back xt_IDLETIMER to 5.10.21 upstream/vanilla version

Conflict resolution was done incorrectly and needs to be redone.
(the registration passes in two different revision one blocks,
 instead of one rev zero, and one rev one, it also erroneously changes
 upstream uapi)

Generated via:
  git cat-file -p remotes/linux-stable/v5.10.21:net/netfilter/xt_IDLETIMER.c > net/netfilter/xt_IDLETIMER.c
  git cat-file -p remotes/linux-stable/v5.10.21:include/uapi/linux/netfilter/xt_IDLETIMER.h > include/uapi/linux/netfilter/xt_IDLETIMER.h

Test: builds, and kernel net tests passes
Bug: 183485987
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I33823ddbd139dc7a435388d22ae76966d2bdd2a7