[4254] Moved -f option in perfdhcp help to common options.

Previously -f option was listed in DHCPv6 only options.

src/bin/perfdhcp/command_options.cc

@@ -961,6 +961,11 @@ CommandOptions::usage() const {
         "-E<time-offset>: Offset of the (DHCPv4) secs field / (DHCPv6)\n"
         "    elapsed-time option in the (second/request) template.\n"
         "    The value 0 disables it.\n"
+        "-f<renew-rate>: Rate at which DHCPv4 or DHCPv6 renew requests are sent\n"
+        "    to a server. This value is only valid when used in conjunction\n"
+        "    with the exchange rate (given by -r<rate>).  Furthermore the sum of\n"
+        "    this value and the release-rate (given by -F<rate) must be equal\n"
+        "    to or less than the exchange rate.\n"
         "-h: Print this help.\n"
         "-i: Do only the initial part of an exchange: DO or SA, depending on\n"
         "    whether -6 is given.\n"
@@ -1008,11 +1013,6 @@ CommandOptions::usage() const {
         "\n"
         "DHCPv6 only options:\n"
         "-c: Add a rapid commit option (exchanges will be SA).\n"
-        "-f<renew-rate>: Rate at which DHCPv4 or DHCPv6 renew requests are sent\n"
-        "    to a server. This value is only valid when used in conjunction\n"
-        "    with the exchange rate (given by -r<rate>).  Furthermore the sum of\n"
-        "    this value and the release-rate (given by -F<rate) must be equal\n"
-        "    to or less than the exchange rate.\n"
         "-F<release-rate>: Rate at which IPv6 Release requests are sent to\n"
         "    a server. This value is only valid when used in conjunction with\n"
         "    the exchange rate (given by -r<rate>).  Furthermore the sum of\n"