INN 2.2.2: server_init should take 0 for default port

[Jonathan Kamens]

It should not be necessary for every News reader in existence to have
to write the same code to call getservbyname() to find out the NNTP
port.  This code should be centralized in the libinn version of
server_init, and clients should be able to specify a port number of 0
to get the default port.

It is certainly a step backwards from the old, pre-INN clientlib.c not
to have this functionality, since that old version did do the
getservbyname().

  Jonathan Kamens