Linux 6.8 compat: implement strlcpy fallback

Linux has removed strlcpy in favour of strscpy. This implements a
fallback implementation of strlcpy for this case.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Sponsored-by: https://despairlabs.com/sponsor/
Closes #15805
(cherry picked from commit 7466e09a49)

include/sys/zfs_context.h

@@ -57,6 +57,7 @@ extern "C" {
 #include <sys/disp.h>
 #include <sys/debug.h>
 #include <sys/random.h>
+#include <sys/string.h>
 #include <sys/strings.h>
 #include <sys/byteorder.h>
 #include <sys/list.h>