Ever since the first commit to this git repository, the base DDF files
have been called BaseTypes_IETF_RFC3588.ddf and Base_IETF_RFC3588.ddf
while the documentation still referred to presumably prior names
DiameterBaseTypes.ddf and DiameterBaseAVPs.ddf

Let's fix this discrepancy.

Signed-of-by: Harald Welte <laforge@gnumonks.org>
Change-Id: Ie9f4fea520f03c1659682357e69ffe8325f9b935