tap: fix the tun sndbuf value for kernel 4.20 and later

tap: fix the tun sndbuf value for kernel 4.20 and later

Type: fix

From kernel 4.20, xdp support has been added in tun_sendmsg.
If sndbuf == INT_MAX, kernel executes xdp data path
for tun driver which assumes packets are ethernet frames.
This patch is avoiding the xdp data path in kernel by setting
the sendbuf value < INT_MAX.

Signed-off-by: Mohsin Kazmi <sykazmi@cisco.com>
Change-Id: Ia4aa54b177b96d56a2d513d18d26ca01d5b88929
(cherry picked from commit 4834a66b7b3ef73e486c40ea9d8e36cc2e09c473)