(#21258) Update link to LSB exit code documentation

Link to linuxfoundation.org, as the content had moved and the
refspecs.freestandards.org domain can no longer be resolved by DNS.

Also updated to link to latest LSB release (4.1.0).
Merge pull request #1989 from 3flex/fix/master/21258-stale-LSB-links

(#21258) Update link to LSB exit code documentation