nat: fix nat64 disable
nat: fix nat64 disable

 - we should not copy and iterate over the pool underlying vector, as
   slots can be freed (ie in the freelist).
 - delete interface instead of adding them again
 - fix the log message

Type: fix

Change-Id: If0a7a2f475b4f40793eb29ea80a9d29fe5d1bcb9
Signed-off-by: Benoît Ganne <38aad8ffcfa407b890d258e568f161530f66882d@cisco.com>

FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp