manpages: correct erroneous markup

Text paragraphs should use .PP, since .TP makes it a list item with
indented description.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/extensions/libip6t_HL.man b/extensions/libip6t_HL.man
index bf46881..050641f 100644
--- a/extensions/libip6t_HL.man
+++ b/extensions/libip6t_HL.man
@@ -4,7 +4,7 @@
 any cost. This target is only valid in
 .B mangle
 table.
-.TP
+.PP
 .B Don't ever set or increment the value on packets that leave your local network!
 .TP
 .BI "--hl-set " "value"