Enabled TCP_CORK when sending a file

[tanguilp]

The TCP option TCP_CORK can be used to coalesce headers with the file being sent with the sendfile syscall:

If you plan to use sendfile() for sending files to a TCP socket, but need to send some header data in front of the file contents, you will find it useful to employ the TCP_CORK option, described in tcp(7), to minimize the number of packets and to tune performance

(from the manual of sendfile for Linux - implementations differ between OSes).

It'd be nice to enable it when sending file, although this might be a bit hard to pass the needed parameters to ranch because we need:

• to enabled it before sending the headers
• to disable it after calling sendfile

It also doesn't seem to be supported in inet, but only in the OTP22+ socket module.