restore sending of optional MM info messages

Since commit 2483f1b050496eda7f8707327204251c57212906 the function
gsm48_tx_mm_info() was not called anymore. No MM info messages were
transmitted to phones even if MM info messages were enabled via VTY.

With this commit, we call gsm48_tx_mm_info() after successfully
processing an IMSI ATTACH location update.

Change-Id: Ice5963d84253eb8c803cd2dfa8b25a4db5382827
Related: OS#2850
3 files changed