[MGW NAT] Implement 'nationalize' as inverse operation of 'internationalize'
[MGW NAT] Implement 'nationalize' as inverse operation of 'internationalize'

This is required for MO calls from MSC -> MGW, where the called number
has a international type number and needs to become a national one.

aerosol/osmo_ss7,systra/osmo_ss7,Shadytel/osmo_ss7,aerosol/osmo_ss7,0x7678/osmo_ss7