security/knock/pkg-descr: correction, changes

De-duplicate 'port-hits port-hits'.

Whilst here, reword things slightly.

security/knock/pkg-descr

@@ -1,9 +1,9 @@
-knockd is a port-knock server. It listens to all traffic on an ethernet
-(or PPP) interface, looking for special "knock" sequences of port-hits.
+knockd is a port-knock server.  It monitors all traffic on an Ethernet (or PPP)
+interface for special "knock" sequences of port-hits.
 
-A client makes these port-hits by sending a TCP (or UDP) packet to a
-port on the server. This port need not be open -- since knockd listens
-at the link-layer level, it sees all traffic even if it's destined for
-a closed port. When the server detects a specific sequence of port-hits
-port-hits, it runs a command defined in its configuration file. This
-can be used to open up holes in a firewall for quick access.
+A client makes these port-hits by sending a TCP (or UDP) packet to a port on
+the server.  The port need not be open -- since knockd monitors at the
+link-layer level, it detects all traffic, even if destined for a closed port.
+When the server detects a specific sequence of port-hits, it runs a command
+defined in its configuration file.  The command can be used to open holes in a
+firewall, for quick access.