Fixed memory allocation for struct dirent

While porting clixon to the RTOS Blackberry QNX there was memory corruption while reading the yang models from the disk.
Debugging led to the function `clicon_file_dirent` in `clixon_file.c` in which the `struct dirent` is copied into an array.
According to the UNIX `struct dirent` [documentation](https://man7.org/linux/man-pages/man0/dirent.h.0p.html):
>  The name of an array of char of an unspecified size should not be
>  used as an lvalue. Use of:
>
>           sizeof(d_name)
>
>  is incorrect; use:
>
>          strlen(d_name)
>
>      instead.

I adjusted the memory allocation to take the `strlen(dent->d_name)` into account.

lib/src/clixon_file.c

@@ -50,7 +50,8 @@
 #include <sys/param.h>
 #include <unistd.h>
 #include <netinet/in.h>
- 
+#include <stddef.h>
+
 /* cligen */
 #include <cligen/cligen.h>
 
@@ -103,6 +104,7 @@ clicon_file_dirent(const char     *dir,
    DIR           *dirp;
    int            res;
    int            nent;
+   int            direntStructSize;
    regex_t        re;
    char           errbuf[128];
    char           filename[MAXPATHLEN];
@@ -143,12 +145,13 @@ clicon_file_dirent(const char     *dir,
 	   if ((type & st.st_mode) == 0)
 	       continue;
        }
-       if ((tmp = realloc(new, (nent+1)*sizeof(*dvecp))) == NULL) {
+       direntStructSize = offsetof(struct dirent, d_name) + strlen(dent->d_name) + 1;
+       if ((tmp = realloc(new, (nent+1)*direntStructSize)) == NULL) {
 	   clicon_err(OE_UNIX, errno, "realloc");
 	   goto quit;
        }
        new = tmp;
-       memcpy(&new[nent], dent, sizeof(*dent));
+       memcpy(&new[nent], dent, direntStructSize);
        nent++;
 
    } /* while */