s4-torture: fix format-truncation warning in smb2 session tests.

s4-torture: fix format-truncation warning in smb2 session tests.

../source4/torture/smb2/session.c: In function ‘test_session_reauth5’:
../source4/torture/smb2/session.c:645:36: error: ‘\file.dat’ directive output may be truncated writing 9 bytes into a region of size between 1 and 256 [-Werror=format-truncation=]
  snprintf(fname, sizeof(fname), "%s\\file.dat", dname);
                                    ^~~~~~~~~~
../source4/torture/smb2/session.c:645:2: note: ‘snprintf’ output between 10 and 265 bytes into a destination of size 256
  snprintf(fname, sizeof(fname), "%s\\file.dat", dname);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../source4/torture/smb2/session.c:696:38: error: ‘\file2.dat’ directive output may be truncated writing 10 bytes into a region of size between 1 and 256 [-Werror=format-truncation=]
  snprintf(fname2, sizeof(fname2), "%s\\file2.dat", dname);
                                      ^~~~~~~~~~~
../source4/torture/smb2/session.c:696:2: note: ‘snprintf’ output between 11 and 266 bytes into a destination of size 256
  snprintf(fname2, sizeof(fname2), "%s\\file2.dat", dname);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13437

Guenther

Signed-off-by: Guenther Deschner <gd@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
(cherry picked from commit 5729898248041794ffdd0b769332e015baf12cce)