vty: add 'msisdn' as alias for 'extension'

Rationale: in the HLR, it is called 'msisdn' after the database column, so a
user going back and forth between osmo-hlr and osmo-msc would appreciate being
able to type 'msisdn' in the MSC's vty as well.

Change-Id: I7b46f9736421e8edd8a95ae89e025ebe486fde4c
1 file changed