[NET] net/core: Fix error handling

Upon failure to register "ptype" procfs entry, "softnet_stat" was not
removed, and an incorrect attempt was made to remove the "ptype" entry.

Signed-off-by: Josef 'Jeff' Sipek <jsipek@cs.sunysb.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>