net/smc: fix limit_smc_hs sysctl on big-endian architecture

net->smc.limit_smc_hs is a bool, but its sysctl entry uses
proc_dointvec_minmax() with .maxlen = sizeof(int), so the handler
accesses four bytes at the address of a one-byte field.

On little-endian this works with the extra bytes being written in struct
padding. On big-endian (tested on s390x) the bool sits at the most
significant byte of the int therefore the bool stays false and the "1"
goes into padding. The sysctl reads back 1 but SMC sockets created
afterwards see limit_smc_hs as disabled.

Fix this by using proc_dobool() handler and adjust the maxlen to the
right value.

Fixes: f8406a2fd279 ("net/smc: add sysctl for smc_limit_hs")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Link: https://patch.msgid.link/20261028225350.3753-1-fmancera@suse.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>