Move CAddress to protocol.[ch]pp

This commit does *not* and should not modify *any* code, it only moves
it from net.h and splits it across protocol.cpp and protocol.hpp.

Signed-off-by: Giel van Schijndel <me@mortis.eu>
Merge commit '33e28c9948336784324cf5c7248ce608b93dbfde' into namecoin_merge_v0.8
Namecoin: fix declaration of GetDefaultPort