[Coverity CID :195921]Null pointer dereferences in /tests/net/tcp/src/main.c

[aasthagr]

Static code scan issues seen in File: /tests/net/tcp/src/main.c
Category: Null pointer dereferences
Function: setup_ipv6_tcp_long
Component: Tests
CID: 195921
Please fix or provide comments to square it off in coverity in the link: https://scan9.coverity.com/reports.htm#v32951/p12996

[jukkar]

Similar issues as in #14412 so I will fix it in same PR.