sockstat: split FreeBSD, NetBSD and Linux implementations (#12040)

* sockstat: split FreeBSD, NetBSD and Linux implementations

---------

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>
Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: Juri Dispan <juri.dispan@posteo.net>
Co-authored-by: cyqsimon <28627918+cyqsimon@users.noreply.github.com>

pages/linux/sockstat.md

@@ -0,0 +1,29 @@
+# sockstat
+
+> List open Internet or UNIX domain sockets.
+> See also: `netstat`.
+> More information: <https://manned.org/sockstat>.
+
+- Show information for IPv4 and IPv6 sockets for both listening and connected sockets:
+
+`sockstat`
+
+- Show information for IPv[4]/IPv[6] sockets [l]istening on specific [p]orts using a specific p[R]otocol:
+
+`sockstat -{{4|6}} -l -R {{tcp|udp|raw|unix}} -p {{port1,port2...}}`
+
+- Also show [c]onnected sockets and [u]nix sockets:
+
+`sockstat -cu`
+
+- Only show sockets of the specified `pid` or process:
+
+`sockstat -P {{pid|process}}`
+
+- Only show sockets of the specified `uid` or user:
+
+`sockstat -U {{uid|user}}`
+
+- Only show sockets of the specified `gid` or group:
+
+`sockstat -G {{gid|group}}`