net/librespeed-cli: Update to 1.0.7

Also add some definitions to GO_BUILDFLAGS to properly fill out the output of
librespeed-cli --version. These values are also used in User-Agent when
accessing speedtest server.

PR: 247971
Reported by: Dries Michiels <driesm.michiels@gmail.com> (maintainer)
Reviewed by: meta (myself)