net/smc: Introduce a sysctl for setting SMC-R buffer type

mainline inclusion
from mainline-v6.0-rc1
commit 4bc5008e
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I76JHC
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/smc?id=4bc5008e4387106215b50ae1a4ac2467455725ca



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This patch introduces the sysctl smcr_buf_type for setting
the type of SMC-R sndbufs and RMBs.

Valid values includes:

- SMCR_PHYS_CONT_BUFS, which means use physically contiguous
  buffers for better performance and is the default value.

- SMCR_VIRT_CONT_BUFS, which means use virtually contiguous
  buffers in case of physically contiguous memory is scarce.

- SMCR_MIXED_BUFS, which means first try to use physically
  contiguous buffers. If not available, then use virtually
  contiguous buffers.

Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Litao Jiao <jiaolitao@sangfor.com.cn>