This enables SO_REUSEPORT [1] for clcsock when it is set on smc socket,
so that some applications which uses it can be transparently replaced
with SMC. Also, this helps improve load distribution.

Here is a simple test of NGINX + wrk with SMC. The CPU usage is collected
on NGINX (server) side as below.

Disable SO_REUSEPORT:

05:15:33 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
05:15:34 PM  all    7.02    0.00   11.86    0.00    2.04    8.93    0.00    0.00    0.00   70.15
05:15:34 PM    0    0.00    0.00    0.00    0.00   16.00   70.00    0.00    0.00    0.00   14.00
05:15:34 PM    1   11.58    0.00   22.11    0.00    0.00    0.00    0.00    0.00    0.00   66.32
05:15:34 PM    2    1.00    0.00    1.00    0.00    0.00    0.00    0.00    0.00    0.00   98.00
05:15:34 PM    3   16.84    0.00   30.53    0.00    0.00    0.00    0.00    0.00    0.00   52.63
05:15:34 PM    4   28.72    0.00   44.68    0.00    0.00    0.00    0.00    0.00    0.00   26.60
05:15:34 PM    5    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
05:15:34 PM    6    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
05:15:34 PM    7    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00

Enable SO_REUSEPORT:

05:15:20 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
05:15:21 PM  all    8.56    0.00   14.40    0.00    2.20    9.86    0.00    0.00    0.00   64.98
05:15:21 PM    0    0.00    0.00    4.08    0.00   14.29   76.53    0.00    0.00    0.00    5.10
05:15:21 PM    1    9.09    0.00   16.16    0.00    1.01    0.00    0.00    0.00    0.00   73.74
05:15:21 PM    2    9.38    0.00   16.67    0.00    1.04    0.00    0.00    0.00    0.00   72.92
05:15:21 PM    3   10.42    0.00   17.71    0.00    1.04    0.00    0.00    0.00    0.00   70.83
05:15:21 PM    4    9.57    0.00   15.96    0.00    0.00    0.00    0.00    0.00    0.00   74.47
05:15:21 PM    5    9.18    0.00   15.31    0.00    0.00    1.02    0.00    0.00    0.00   74.49
05:15:21 PM    6    8.60    0.00   15.05    0.00    0.00    0.00    0.00    0.00    0.00   76.34
05:15:21 PM    7   12.37    0.00   14.43    0.00    0.00    0.00    0.00    0.00    0.00   73.20

Using SO_REUSEPORT helps the load distribution of NGINX be more
balanced.

[1] https://man7.org/linux/man-pages/man7/socket.7.htmlSigned-off-by: Tony Lu <tonylu@linux.alibaba.com>
Acked-by: Wenjia Zhang <wenjia@linux.ibm.com>
Link: https://lore.kernel.org/r/20220922121906.72406-1-tonylu@linux.alibaba.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>