add osmo-mgw --vty-ref-xml: dump VTY ref XML to stdout

Add only a long option to not clutter the cmdline namespace.

To add a long option without a short letter is slightly complex: use the 'flag'
and 'val' mechanism as in 'man 3 getopt' to write an option index to
long_option.

Depends: Ic74bbdb6dc5ea05f03c791cc70184861e39cd492 (libosmocore)
Change-Id: Ia988ea1c3f5169bdb4d21f2f05933665711cfcbf
1 file changed