man: add some notes to kxdpgun

doc/man/kxdpgun.8in

@@ -107,6 +107,11 @@ Linux kernel 4.18+ is required.
 .sp
 The utility has to be executed under root or with these capabilities:
 CAP_NET_RAW, CAP_NET_ADMIN, CAP_SYS_ADMIN, CAP_SYS_RESOURCE, CAP_SETPCAP.
+.sp
+Sending USR1 signal to a running process triggers current statistics dump
+to the standard output.
+.sp
+The utility allocates source UDP/TCP ports from the range 2000\-65535.
 .SH EXIT VALUES
 .sp
 Exit status of 0 means successful operation. Any other exit status indicates

doc/man_kxdpgun.rst

@@ -88,6 +88,11 @@ Linux kernel 4.18+ is required.
 The utility has to be executed under root or with these capabilities:
 CAP_NET_RAW, CAP_NET_ADMIN, CAP_SYS_ADMIN, CAP_SYS_RESOURCE, CAP_SETPCAP.
 
+Sending USR1 signal to a running process triggers current statistics dump
+to the standard output.
+
+The utility allocates source UDP/TCP ports from the range 2000-65535.
+
 Exit values
 -----------