net/fspd: revive

• stage
• add a static pkg-plist
• add DOCS knob
• do not build SGML documentation (jade fails)
• only install man pages for client commands if CLIENTS option is set

Changes from me:

• flip NOCLIENTS option into a CLIENTS option
• drop MLINKS files
• use @sample
• other minor Makefile changes

PR: 193393
Submitted by: Radim Kolar