ip/defrag: fix processing of last short fragment

TFTP'ing a file of size 1747851 bytes with CONFIG_IP_DEFRAG and
CONFIG_TFTP_BLOCKSIZE set to 4096 fails with a timeout, because
the last fragment is not taken into account. This patch fixes
IP fragments having less than 8 bytes of payload.
Signed-off-by: NStephane Fillod <stephane.fillod@grassvalley.com>
Acked-by: NAlessandro Rubini <rubini@gnudd.com>
Signed-off-by: NBen Warren <biggerbadderben@gmail.com>

net/net.c

@@ -1201,7 +1201,8 @@ static IP_t *__NetDefragment(IP_t *ip, int *lenp)
 		h = payload + h->next_hole;
 	}
 
-	if (offset8 + (len / 8) <= h - payload) {
+	/* last fragment may be 1..7 bytes, the "+7" forces acceptance */
+	if (offset8 + ((len + 7) / 8) <= h - payload) {
 		/* no overlap with holes (dup fragment?) */
 		return NULL;
 	}