Merge branch 'isdn-null-deref'

Merge branch 'isdn-null-deref'

Karsten Keil says:

====================
Fix potential NULL pointer access and memory leak in ISDN layer2 functions

Insu Yun did brinup the issue with not checking the skb_clone() return
value in the layer2 I-frame ull functions.
This series fix the issue in a way which avoid protocol violations/data loss
on a temporary memory shortage.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>