tweaked default delivery map size

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1594083 13f79535-47bb-0310-9956-ffa450edef68
use uint16_t instead of size_t to reference other nodes inside pn_data_t

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1594084 13f79535-47bb-0310-9956-ffa450edef68