net/p5-Net-Server requires dependency on p5-IO-Multiplex

When use Net::Server::Multiplex, IO::Multiplex is required:

[~/postgresql-postfix] edwin@k7>./test.pl
Module IO::Multiplex is required for Multiplex. at /usr/local/lib/perl5/site_perl/5.8.8/Net/Server/Multiplex.pm line 32.

PR: ports/96175