net: tunnels - enable module autoloading

[ Upstream commit f98f89a0 ]

Enable the module alias hookup to allow tunnel modules to be autoloaded on demand.

This is in line with how most other netdev kinds work, and will allow userspace
to create tunnels without having CAP_SYS_MODULE.

Signed-off-by: Tom Gundersen <teg@jklm.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>