Add MSG_SPLICE_PAGES from Linux 6.5 to bits/socket.h

[Dmitry V. Levin]

On Fri, Oct 13, 2023 at 10:51:09PM +0000, Joseph Myers wrote:
> Linux 6.5 adds a constant MSG_SPLICE_PAGES.  Add this constant to
> glibc's bits/socket.h.

It's an internal flag that's cleared on entering syscalls.


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