ipv6: sit: Replace deprecated strcpy with strscpy

ipv6: sit: Replace deprecated strcpy with strscpy

strcpy() has been deprecated [1] because it performs no bounds checking
on the destination buffer, which can lead to buffer overflows. Replace
it with the safer strscpy().  Use the two-argument version of strscpy()
to copy 'parms->name' in ipip6_tunnel_locate().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20260227004541.798966-3-thorsten.blum@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>