Comply with expected header for generated Go code

[mdlayher]

Hello! I'm using c-for-go for several projects, and thus far have had to add workarounds to avoid linting code generated by this tool. I just realized that the header generated by the tool doesn't quite comply with the recognized format for generated Go code, as defined in this issue: golang/go#13560.

This resolves that problem and allows linting tools to recognize and skip code generated by this tool.

Before:

✔ ~/src/github.com/mdlayher/devlink [master|…2] 
10:01 $ golint ./...
internal/dlh/const.go:64:2: don't use underscores in Go names; const __CmdMax should be _CmdMax
internal/dlh/const.go:183:2: const AttrDpipeHeaderId should be AttrDpipeHeaderID
internal/dlh/const.go:189:2: const AttrDpipeFieldId should be AttrDpipeFieldID
internal/dlh/const.go:197:2: const AttrResourceId should be AttrResourceID
internal/dlh/const.go:206:2: const AttrDpipeTableResourceId should be AttrDpipeTableResourceID
internal/dlh/const.go:208:2: don't use underscores in Go names; const __AttrMax should be _AttrMax
internal/dlh/const.go:238:6: type devlinkDpipeFieldEthernetId should be devlinkDpipeFieldEthernetID
internal/dlh/const.go:250:2: const DpipeFieldIpv4DstIp should be DpipeFieldIpv4DstIP
internal/dlh/const.go:258:2: const DpipeFieldIpv6DstIp should be DpipeFieldIpv6DstIP
internal/dlh/const.go:262:6: type devlinkDpipeHeaderId should be devlinkDpipeHeaderID

After:

✔ ~/src/github.com/mdlayher/devlink [master|…2]
10:01 $ go generate ./...
--2018-06-01 10:01:11--  https://raw.githubusercontent.com/torvalds/linux/master/include/uapi/linux/devlink.h
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 151.101.184.133
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|151.101.184.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 8216 (8.0K) [text/plain]
Saving to: ‘devlink.h’

devlink.h                        100%[=========================================================>]   8.02K  --.-KB/s    in 0.001s

2018-06-01 10:01:12 (13.0 MB/s) - ‘devlink.h’ saved [8216/8216]

  processing dlh.yml done.
✔ ~/src/github.com/mdlayher/devlink [master|✚ 1…2]
10:01 $ golint ./...

[xlab]

Cool, I'm glad that the changes required to comply are not that harsh as I expected :)