avahi-gobject: Use string.length instead of deprecated string.size()
avahi-gobject: Use string.length instead of deprecated string.size()

Fixes bug 648506.

GNOME/vala,Distrotech/vala,frida/vala,kamanashisroy/aroop,rvu95/vala,spidermonkdust/vala,flobrosch/vala-fixes,severinh/vala,Distrotech/vala,severinh/vala,GNOME/vala,frida/vala,tjol/vala-tjol,rvu95/vala,playya/vala,Distrotech/vala,playya/vala,flobrosch/vala-fixes,frida/vala,frida/vala,tjol/vala-tjol,GNOME/vala,kamanashisroy/aroop,xdave/pvala,spidermonkdust/vala,jessevdk/vala,playya/vala,severinh/vala,spidermonkdust/vala,GNOME/vala,kamanashisroy/aroop,jessevdk/vala,jessevdk/vala,frida/vala,flobrosch/vala-fixes,tjol/vala-tjol,rvu95/vala