[NETFILTER]: {arp,ip,ip6}_tables: proper error recovery in init path

Neither of {arp,ip,ip6}_tables cleans up behind itself when something goes
wrong during initialization.

Noticed by Rennie deGraaf <degraaf@cpsc.ucalgary.ca>

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>