rc: Rename jail's rc default variables

rc: Rename jail's rc default variables

- Also add the remaining sysctls that were not handled. Here's
  the current list:

      jail_default_set_hostname_allow       (default: enabled)
      jail_default_socket_unixiproute_only  (default: enabled)
      jail_default_sysvipc_allow            (default: disabled)
      jail_default_chflags_allow            (default: disabled)
      jail_default_raw_sockets_allow        (default: disabled)

- You can override the default by editing rc.conf(5) as usual, please
  make sure you adjust these variables if you're using them.