ports-mgmt/synth: Update to 2.11 release

This fixes https://github.com/jrmarino/synth/issues/193
(sys/sys/param.h in freebsd/main loses comment after __FreeBSD_version)

MFH: 2021Q2
(cherry picked from commit a53b9c858eb613ea9f1e79d0b31655d747cc5275)