defconfig: sdm670: Enable missing networking options

Android Kernel Net Testing requires additional configuration options
to work properly. Enable the following-
        SYN_COOKIES
        INET_UDP_DIAG
        IP_SCTP
        INET_SCTP_DIAG

Change-Id: I89f0fdaa6adb6ae532933b2b89eed7e7068596de
Signed-off-by: Chinmay Agarwal <chinagar@codeaurora.org>