net/tcpslice: update to 1.5

This update chase a long standing security update in tcpslice. It also
corrects the installation of the binary in ${PREFIX}/bin instead of sbin,
follow the versioning scheme of upstream and add PORTEPOCH.

Security: 61f416ff-aa00-11ec-b439-000d3a450398
Security: CVE-2021-41043
(cherry picked from commit d437b53dc706e83f97c9dc81b99773e623936870)