Ignore invalid IPs in X-Forwarded-For when trusted proxies are configured.

What does this MR do?

Catches IPAddr::InvalidAddressError exceptions in trusted_proxy? when a) a trusted proxy is set up in the gitlab config and b) an invalid IP address is passed to the method (e.g. one with a port attached). When caught, returns false from the method. Prevents a 500 error in this situation.

What are the relevant issue numbers?

Closes gitlab-org/gitlab-ce#20466.

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• [N/A] Documentation created/updated
• [N/A] API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together