vlc_config_set: use dgettext() explicitly
vlc_config_set: use dgettext() explicitly

This is a cosmetic change at this point as _() invokes dgettext(). This
is just a small step toward supporting out-of-tree plugins. These will
need to use their own text domain.

jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,xkfz007/vlc,jomanmuk/vlc-2.1,shyamalschandra/vlc,krichter722/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,xkfz007/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,shyamalschandra/vlc,vlc-mirror/vlc,xkfz007/vlc,krichter722/vlc,shyamalschandra/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,xkfz007/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc,krichter722/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,shyamalschandra/vlc,xkfz007/vlc,vlc-mirror/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,jomanmuk/vlc-2.1,jomanmuk/vlc-2.2