Fix ifaddrs error handling.

An NLMSG_ERROR packet includes an errno value that we should use. Also report
failures to create a socket immediately, rather than falling through to the
send and reporting EBADF.

Bug: http://b/32145516
Bug: http://b/31038971
Test: bionic ifaddr tests on ryu (with broken kernel) and flounder
Change-Id: I84c480c5b75077eb90d40426a9d66d7bffbd3d51