LU-13783 lnet: remove kernel_setsockopt() from lnet_sock_listen()

LU-13783 lnet: remove kernel_setsockopt() from lnet_sock_listen()

Linux 5.8 removes kernel_setsockopt(). In Lustre commit
99d9638d6c0, kernel_setsockopt() was removed from Lustre codes
by using direct access or helper calls. However, the one in
lnet_sock_listen() was not removed. This patch removes it by
using the codes from previously defined kernel_setsockopt()
directly.

Fixes: 99d9638d6c0 ("LU-13783 libcfs: support removal of kernel_setsockopt()")
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Change-Id: I5b74bf113185c0c9af5c81ca6cd346f1be7a4720
Reviewed-on: https://review.whamcloud.com/43207
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>