net/packet: fix overflow in check for tp_reserve

net/packet: fix overflow in check for tp_reserve

When calculating po->tp_hdrlen + po->tp_reserve the result can overflow.

Fix by checking that tp_reserve <= INT_MAX on assign.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
BugLink: https://bugs.launchpad.net/bugs/1678009
CVE-2017-7308
(cherry picked from linux-next commit bcc5364bdcfe131e6379363f089e7b4108d35b70)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>