libnftables: location-based error reporting for chain type

libnftables: location-based error reporting for chain type

Store the location of the chain type for better error reporting.

Several users that compile custom kernels reported that error
reporting is misleading when accidentally selecting
CONFIG_NFT_NAT=n.

After this patch, a better hint is provided:

 # nft 'add chain x y { type nat hook prerouting priority dstnat; }'
 Error: Could not process rule: No such file or directory
 add chain x y { type nat hook prerouting priority dstnat; }
                      ^^^

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>