net/unfs3: Fix build with -fno-common (FreeBSD 13 or later)

• Update MASTER_SITES and WWW as project has moved to GitHub
• Pass maintainership to submitter
• Clean up and reformat Makefile

PR: 258326
Approved by: meta (mentor)
MFH: 2021Q3
Differential Revision: https://reviews.freebsd.org/D32220