Describe the addr, addrlen parameters in gsup_route_find() and (more
commonly used) osmo_gsup_addr_send(). Without this description, it is
easy to get the parameters wrong and have routes not being found, as
shown with debug prints like these:
gsup_route_find: addr, addrlen: "MSC-13-37-00-00-00-00", 21
gsup_route_find: comparing with: "MSC-13-37-00-00-00-00\0", 22
Change-Id: Ib79878970bd07caac6eb921af8ae95403b90a4cb
We also introduce a 'gsup_router' which enables us to route
a transaction to a given VLR. It works based on the SERIAL attribute
communicated at time of the IPA multiplex setup as part of the CCM
sub-protocol.