GSD-2021-1001560 sctp: break out if skb_header_pointer returns NULL in sctp_rcv_ootb

sctp: break out if skbheaderpointer returns NULL in sctprcvootb This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.19.209 by commit...