net-mgmt/ipv6mon: fix installation

Port uses <bsd.prog.mk>, which desires STRIP=${STRIP}, but we have
started to set STRIP=${STRIP_CMD} in MAKE_ENV a while ago.
Override this bogus setting in MAKE_ARGS to fix installation.

MFH:		2026Q2
See also:	D55509
Approved by:	portmgr (build fix blanket)

net-mgmt/ipv6mon/Makefile

@@ -20,7 +20,7 @@ CFLAGS+=	-DIPV6MON_CONF=\\\"${PREFIX}/etc/ipv6mon.conf\\\"
 USERS=		${PORTNAME}
 GROUPS=		${PORTNAME}
 USE_RC_SUBR=	${PORTNAME}
-MAKE_ARGS=	MANDIR=${PREFIX}/share/man/man
+MAKE_ARGS=	MANDIR=${PREFIX}/share/man/man STRIP=${STRIP}
 
 PORTDOCS=	README.TXT \
 		ipv6mon-installation-notes.odt \