prov/sockets: add per domain connection map for sockets level connection.

Sockets provider update.
- Add per domain connection map to manage sockets level connection establishment.
- Update fi_av APIs implementation in sockets provider accordingly.
This destroys the existing map on failure without freeing it.  Restructure to:

tmp = realloc()
if (!tmp)
    return -FI_ENOMEM;

map->size = ...
map->table = tmp