net-mgmt/sdig: Fix build with -fno-common

• Add license information
• Reformat Makefile with portfmt

PR: 259006
Approved by: maintainer timeout (> 2 weeks)
Differential Revision: https://reviews.freebsd.org/D32661

(cherry picked from commit 3436c34cf6a6663dce899fe2d33ffdf3abf841f0)