getifaddrs() can fail transiently with ECONNREFUSED on Linux.
This has been observed with Linux 3.10 when multiple processes
call zmq::tcp_address_t::resolve_nic_name() simultaneously.

Before asserting in this case, make 10 attempts, with exponential
backoff, given by (1 msec * 2^i), where i is the attempt number.

Fixes #2051