Fix compilation of world with WITHOUT_{INET,INET6}_SUPPORT or both set.

Buildworld failed when both WITHOUT_INET6_SUPPORT and INET equivalent were set.
Fix netstat and syslogd by applying appropriate #ifdef INET/INET6 to make world
compile again.

Reviewed by: ngie, hrs, ume
Welcomed by: Michael Dexter (D17040)
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D19418