REORG: connection: uninline the rest of the alloc/free stuff

REORG: connection: uninline the rest of the alloc/free stuff

The remaining large functions are those allocating/initializing and
occasionally freeing connections, conn_streams and sockaddr. Let's
move them to connection.c. In fact, cs_free() is the only one-liner
but let's move it along with the other ones since a call will be
small compared to the rest of the work done there.