net: fix tokenring license

Currently, modular tokenring ("tr") lacks a license and fails to load:

tr: module license 'unspecified' taints kernel.
tr: Unknown symbol proc_net_fops_create

Beacuse of this, no tokenring driver can load if it depends on modular 
tr. Fix this by adding GPL module license as it is in the kernel.

With this fix, tr module loads fine and tms380 driver also loads. Well, 
it does'nt work but that's a different bug.

Signed-off-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: David S. Miller <davem@davemloft.net>