capsicum-test: include SCTP tests

[emaste]

Summary

HAVE_SCTP is #defined in syscalls.h, so move the #ifdef after the
inclusion of the header that #defines it.

Issue https://github.com/google/capsicum-test/issues/60 is open upstream
in case a slightly different version is needed for Linux.

Test Plan

For FreeBSD Jenkins we need to ensure sctp.ko is loaded for this test to be useful. Also I think the test will fail if it is not, and we probably want it to return unsupported instead.