sgsn: use vty cmd `reset sgsn state`.

Cleans most of the sgsn state.
Depends on the SGSN commit I92096f3f6ea49e75676e30e9921d00210bac5382.

Change-Id: Idff3de6f1b8f5cb503edc5c6256ce2bf7ec7aaa2
1 file changed