oslib: fix strlcat's incorrect copying

oslib: fix strlcat's incorrect copying

Fix unittests/oslib/strlcat.c test case failure.

oslib/strlcat.c implementation is incorrect for edge case inputs,
when (dsize-strlen(dst)-1 <= 0). The example below isn't supposed
to be copying anything, but the result is it does copy and
overruns the stack.

This commit replalces oslib/strlcat.c with the original implementation
under BSDL.

--
 # uname
 Linux
 # cat ./test0.c
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include "./oslib/strlcat.h"

 int main(void) {
         char *p, s[10] = "test";
         int size = 200;

         p = calloc(1, size);
         memset(p, 65, size - 1);

         printf("%lu %lu %s\n", sizeof(s), strlen(s), s);
         strlcat(s, p, strlen(s));
         printf("%lu %lu %s\n", sizeof(s), strlen(s), s);

         return 0;
 }
 # gcc -Wall -g ./test0.c ./oslib/strlcat.c
 # ./a.out
 10 4 test
 10 203 testAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
 Segmentation fault (core dumped)

Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>