Print IPv4 address correctly on little-endian systems

[gllghr]

The IPv4 addresses in /proc/tcp are not converted to host order before being printed by the kernel, so they have least-significant byte first on little-endian systems (see https://github.com/torvalds/linux/blob/0f1a7b3fac0583083ca19d4de47403511ced3521/net/ipv4/tcp_ipv4.c#L2460). We need to convert them back to network order when parsing them.

Previous output:

   92: S_IFSOCK mode:777 dev:0,9 ino:1093729 uid:0 gid:0 size:0
       O_RDWR
         SOCK_STREAM
         sockname: AF_INET 1.0.0.127  port: 8586

Fixed output:

   92: S_IFSOCK mode:777 dev:0,9 ino:1093729 uid:0 gid:0 size:0
       O_RDWR
         SOCK_STREAM
         sockname: AF_INET 127.0.0.1  port: 8586

I also added a follow-up commit which improves the error handling in the relevant function and adds tests for it.

ab-pre-push: http://selfservice.jenkins.delphix.com/job/devops-gate/job/master/job/appliance-build-orchestrator-pre-push/2263/

Fixes #1

[gllghr]

cc @sebroy