MINOR: connection: create a new pool for struct sockaddr_storage

MINOR: connection: create a new pool for struct sockaddr_storage

This pool will be used to allocate storage for source and destination
addresses used in connections. Two functions sockaddr_{alloc,free}()
were added and will have to be used everywhere an address is needed.
These ones are safe for progressive replacement as they check that the
existing pointer is set before replacing it. The pool is not yet used
during allocation nor freeing. Also they operate on pointers to pointers
so they will perform checks and replace values. The free one nulls the
pointer.