[AX25] ax25_out: check skb for NULL in ax25_kick()
[AX25] ax25_out: check skb for NULL in ax25_kick()

According to some OOPS reports ax25_kick tries to clone NULL skbs
sometimes. It looks like a race with ax25_clear_queues(). Probably
there is no need to add more than a simple check for this yet.
Another report suggested there are probably also cases where ax25
->paclen == 0 can happen in ax25_output(); this wasn't confirmed
during testing but let's leave this debugging check for some time.

Reported-and-tested-by: Jann Traschewski <1ff1d5ceb421971f93e6626b02a9591b29d7600e@gmx.de>
Signed-off-by: Jarek Poplawski <85e4e0cd35fdfcbe234be29b330d591ff9717625@gmail.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs