Merge branch 'net-rmnet-fix-interface-leak-for-rmnet-module'

Taehee Yoo says:

====================
net: rmnet: fix interface leak for rmnet module

There are two problems in rmnet module that they occur the leak of
a lower interface.
The symptom is the same, which is the leak of a lower interface.
But there are two different real problems.
This patchset is to fix these real problems.

1. Do not allow to have different two modes.
As a lower interface of rmnet, there are two modes that they are VND
and BRIDGE.
One interface can have only one mode.
But in the current rmnet, there is no code to prevent to have
two modes in one lower interface.
So, interface leak occurs.

2. Do not allow to add multiple bridge interfaces.
rmnet can have only two bridge interface.
If an additional bridge interface is tried to be attached,
rmnet should deny it.
But there is no code to do that.
So, interface leak occurs.
====================

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