defconfig: sdm450: 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: I70d9a5ed56a3a30da74e90375c9421dc716d5bbc
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>
Signed-off-by: Chinmay Agarwal <chinagar@codeaurora.org>