net/smc: Replace use of strncpy on NUL-terminated string with strscpy

strncpy is deprecated for use on NUL-terminated strings, as indicated in
Documentation/process/deprecated.rst. strncpy NUL-pads the destination
buffer and doesn't guarantee the destination buffer will be NUL
terminated.

Signed-off-by: James Flowers <bold.zone2373@fastmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Link: https://patch.msgid.link/20250901030512.80099-1-bold.zone2373@fastmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>