Merge branch 'fix-uaf-bugs-caused-by-ax25_release'

Duoming Zhou says:

====================
Fix UAF bugs caused by ax25_release()

The first patch fixes UAF bugs in ax25_send_control, and
the second patch fixes UAF bugs in ax25 timers.
====================

Link: https://lore.kernel.org/r/cover.1648472006.git.duoming@zju.edu.cn


Signed-off-by: Paolo Abeni <pabeni@redhat.com>