Port enabled network mode selection menu to MSIM classes

* MSIM mobile network settings menu will not display network mode
  selection unless world phone is selected. Make it available for GSM
  only as well.

Change-Id: I1bafc6049a7152382af601312361619f2e6256cd
Clean up MSimMobileNetworkSubSettings

* Reduce code duplication from MobileNetworkSettings class from where
  this is originally derived.

Change-Id: Icc31d313351dac53fb4597ec31ec1f121425b3a7