MFC r356527-356528:

MFC r356527-356528:

  vnet: virtualise more network stack sysctls.

  Virtualise tcp_always_keepalive, TCP and UDP log_in_vain.  All three are
  set in the netoptions startup script, which we would love to run for VNETs
  as well.

  While virtualising the log_in_vain sysctls seems pointles at first for as
  long as the kernel message buffer is not virtualised, it at least allows
  an administrator to debug the base system or an individual jail if needed
  without turning the logging on for all jails running on a system.

  Run netoptions startup script in vnet jails.

  People use rc.conf inside vnet jails to configure networking setups.
  Presumably because some sysctl were not virtualised up until r356527 the
  script was not run for vnet jails leaving the rc.conf options without
  effect for non-obvious reasons.  Run the netoptions startup script also
  for VNET jails now to make the rc.conf options work.

PR:		243193