MFH: r528561

security/softether5: fix build on aarch64

Tested on Amazon EC2 A1 instances with FreeBSD/ARM 12 image[1].
Build on mips also should be fixed (not actually tested).

[1] https://aws.amazon.com/marketplace/pp/B081NF7BY7

Sponsored by: HAW International

Approved by: portmgr branket (fix build)