devip: fix use after free in ipifcremmulti()

devip: fix use after free in ipifcremmulti()

closeconv() calls ipifcremmulti() like:

	while((mp = cv->multi) != nil)
		ipifcremmulti(cv, mp->ma, mp->ia);

so we have to defer freeing the entry after doing:

		if((lifc = iplocalonifc(ifc, ia)) != nil)
			remselfcache(f, ifc, lifc, ma);

which accesses the otherwise free'd ia and ma arguments.