net/sched: potential data corruption

The reset_policy() does:
        memset(d->tcfd_defdata, 0, SIMP_MAX_DATA);
        strlcpy(d->tcfd_defdata, defdata, SIMP_MAX_DATA);

In the original code, the size of d->tcfd_defdata wasn't fixed and if
strlen(defdata) was less than 31, reset_policy() would cause memory
corruption.

Please Note:  The original alloc_defdata() assumes defdata is 32
characters and a NUL terminator while reset_policy() assumes defdata is
31 characters and a NUL.  This patch updates alloc_defdata() to match
reset_policy() (ie a shorter string).  I'm not very familiar with this
code so please review carefully.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>