[InterNetNews/inn] 010ee2: innfeed: Fix the build when FD_SETSIZE is unset

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: 010ee22a52889f986806b7abd2b51e4183dc3cc8
      https://github.com/InterNetNews/inn/commit/010ee22a52889f986806b7abd2b51e4183dc3cc8
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2023-07-08 (Sat, 08 Jul 2023)

  Changed paths:
    M innfeed/endpoint.c

  Log Message:
  -----------
  innfeed: Fix the build when FD_SETSIZE is unset

NO_STDIO_FDMAX was not defined.

... and has not been since a long time (when innfeed/msgs.h had it in
INN 2.3).