fix osmo-mgw -s; fixes osmo-mgw.service using -s

Even though osmo-mgw advertises the -s option, the getopt configuration lacks
-s and that option does not work. Thus the osmo-mgw.service file that uses -s
was unable to start.

Add 's' to the getopt configuration, fix -s and hence also fix the .service
file.

Change-Id: I6f298aef73eb3486d04706910e9fdbaaebaf2481
1 file changed