[NET]: Call uninit if necessary in register_netdevice

This patch makes register_netdevice call dev->uninit if the regsitration
fails after dev->init has completed successfully.  Very few drivers use
the init/uninit calls but at least one (drivers/net/wan/sealevel.c) may
leak without this change.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>