Corrected some long-form getopt option-specifiers

[mikehaben69]

The set-imsi, set-mnclen and set-milenage option specifier strings each need a trailing equals sign, otherwise the getopt.getopt() function does not parse the subsequent argument correctly. Symptom is that
python3 sysmo-isim-tool.sja2.py --adm1 12345678 -J 001010000056789
works, but
python3 sysmo-isim-tool.sja2.py --adm1 12345678 --set-imsi 001010000056789
does not (and similarly -N works but --set-mnclen does not).

[laf0rge]

Thanks! Please note that github is just a read-only mirror of the tool, which is maintained at https://gitea.sysmocom.de/sysmocom/sysmo-usim-tool

It would be great if you could raise your PR there, so we can review + merge there before it will be mirrored back to github as a read-only mirror. Thanks!