Handle explicitely all enum values in 'switch' on AddrInfo tag

Handle explicitely all enum values in 'switch' on AddrInfo tag
(reported by Florian)

Note that Addr_Undescribed will cause an assert if such
an undescribed addrinfo is pretty printed, as normally
such addrinfo should always be described before being pretty printed.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14558