xfrm: fix the condition on x->pcpu_num in xfrm_sa_len

pcpu_num = 0 is a valid value. The marker for "unset pcpu_num" which
makes copy_to_user_state_extra not add the XFRMA_SA_PCPU attribute is
UINT_MAX.

Fixes: 1ddf991 ("xfrm: Add support for per cpu xfrm state handling.")
Signed-off-by: Sabrina Dubroca <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Signed-off-by: Steffen Klassert <[email protected]>

Author: qsn

net/xfrm/xfrm_user.c

@@ -3676,7 +3676,7 @@ static inline unsigned int xfrm_sa_len(struct xfrm_state *x)
 	}
 	if (x->if_id)
 		l += nla_total_size(sizeof(x->if_id));
-	if (x->pcpu_num)
+	if (x->pcpu_num != UINT_MAX)
 		l += nla_total_size(sizeof(x->pcpu_num));
 
 	/* Must count x->lastused as it may become non-zero behind our back. */