MFC r339542:
Retire IPFIREWALL_NAT64_DIRECT_OUTPUT kernel option. And add ability to switch the output method in run-time. Also document some sysctl variables that can by changed for NAT64 module. NAT64 had compile time option IPFIREWALL_NAT64_DIRECT_OUTPUT to use if_output directly from nat64 module. By default is used netisr based output method. Now both methods can be used, but they require different handling by rules. Obtained from: Yandex LLC Sponsored by: Yandex LLC Differential Revision: https://reviews.freebsd.org/D16647