net: drivers: Slip can get the MTU set on it's interface

No need to store the mtu locally as the network interface already holds
it.

Change-Id: I4a1c3d164eefa28622dcb6cd510a66a825c3d9fb
Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>
1 file changed