Update to 1.2.4.

• 2x crypto throughput on x64 using Salsa20/12 assembler implementation from DJB.
• only default managed routes are bifurcated, most people will not notice.
• reduce memory usage of credentials.
• improve path selection and prioritisation.
• various build cleanups.

Changelog: https://github.com/zerotier/ZeroTierOne/releases/tag/1.2.4

PR: 218926
Submitted by: Dave Cottlehuber <dch@skunkwerks.at> (maintainer)