net/smc: Cork when sendpage with MSG_SENDPAGE_NOTLAST flag

mainline inclusion
from mainline-v5.18-rc1
commit be9a16cc
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I78OQ2
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/smc?id=be9a16cccaefac23cb16909e04bb65e62e09d515

--------------------------------

This introduces a new corked flag, MSG_SENDPAGE_NOTLAST, which is
involved in syscall sendfile() [1], it indicates this is not the last
page. So we can cork the data until the page is not specify this flag.
It has the same effect as MSG_MORE, but existed in sendfile() only.

This patch adds a option MSG_SENDPAGE_NOTLAST for corking data, try to
cork more data before sending when using sendfile(), which acts like
TCP's behaviour. Also, this reimplements the default sendpage to inform
that it is supported to some extent.

[1] https://man7.org/linux/man-pages/man2/sendfile.2.html



Signed-off-by: Tony Lu <tonylu@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Litao Jiao <jiaolitao@sangfor.com.cn>