net: Update dahdi for alloc_netdev() api change in 3.17+

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c835a677331495cf137a7f8a023463afd9f0~

Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>
Acked-by: Shaun Ruffell <sruffell@digium.com>