osdmap: use shared_ptr for addrs, addr vectors

osdmap: use shared_ptr for addrs, addr vectors

We share a lot of identical addresses between map versions because they
don't tend to change very often.  Instead of having a separate copy for
every map, use shared_ptr and share references.  Also use a reference for
the entire addr vector(s) in case no addrs differ at all.

Create new encode/decode macros for vector< shared_ptr<T> >.

Signed-off-by: Sage Weil <sage@newdream.net>