Update internal.h

[liujinhui-job]

When two threads concurrently invoke the socket function, the absence of lock protection in citp_fdinfo_init may occasionally result in identical sequence numbers (seq) being assigned to different file descriptor information (fdi) entries.

[ol-alexandra]

The change itself looks reasonable, but the commit log should include more details, I think. The description of the pull request includes all these details, but the git commit log does not.