exec: increase BINPRM_BUF_SIZE to 256

exec: increase BINPRM_BUF_SIZE to 256

Large enterprise clients often run applications out of networked file
systems where the IT mandated layout of project volumes can end up leading
to paths that are longer than 128 characters.  Bumping this up to the next
order of two solves this problem in all but the most egregious case while
still fitting into a 512b slab.

Link: http://lkml.kernel.org/r/20181112160956.GA28472@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Ben Woodard <woodard@redhat.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>