[NETFILTER]: more verbose return codes from nf_{log,queue}
This adds EEXIST to distinguish between the following return values:
0: nobody was registered, registration successful
EEXIST: the exact same handler was already registered, no registration
required
EBUSY: somebody else is registered, registration unsuccessful.
Signed-off-by: Harald Welte <laforge@netfilter.org> Signed-off-by: David S. Miller <davem@davemloft.net>