lesspipe: Allow zstd to operate on a symlink

By default zstd refuses to operate on symlinks, so for example
`zless /var/crash/vmcore.last.zst` failed to view the uncompressed core
file.  Add -f to the zstd command line to allow operation on symlinks.

Reviewed by:	delphij
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D55101

usr.bin/less/lesspipe.sh

@@ -21,7 +21,7 @@ case "$1" in
 		exec lzma -d -c "$1"	2>/dev/null
 		;;
 	*.zst)
-		exec zstd -d -q -c "$1"	2>/dev/null
+		exec zstd -d -q -c -f "$1"	2>/dev/null
 		;;
 	*)	exec cat "$1"		2>/dev/null
 		;;