net/iaxmodem: Initiate sunset

This port hasn't been updated despite there being four 1.3.x releases
since 2016 (there is nothing in Bugzilla on that either), and it depends
on GCC 9 which has been end-of-lifed upstream nearly two years ago.

Faxes aren't used much any more and apparently there is no need/use for
this port.

Mark deprecated with an expiration date of 2024-05-28. On the way reset
maintainer to ports@.

Approved by:	maintainer

net/iaxmodem/Makefile

@@ -4,10 +4,13 @@ PORTREVISION=	11
 CATEGORIES=	net comms
 MASTER_SITES=	SF/${PORTNAME}/${PORTNAME}/${PORTNAME}-${PORTVERSION}
 
-MAINTAINER=	stucchi@gufi.org
+MAINTAINER=	ports@FreeBSD.org
 COMMENT=	Software modem that connects to IAX channel
 WWW=		https://iaxmodem.sourceforge.net/
 
+DEPRECATED=	outdated and uses end-of-life version of GCC
+EXPIRATION_DATE=2024-05-28
+
 LIB_DEPENDS=	libtiff.so:graphics/tiff
 
 USES=		compiler:features perl5