MINOR: freq_ctr: unify freq_ctr and freq_ctr_period into freq_ctr

Both structures are identical except the name of the field starting
the period and its description. Let's call them all freq_ctr and the
period's start "curr_tick" which is generic.

This is only a temporary change and fields are expected to remain
the same with no code change (verified).
diff --git a/admin/wireshark-dissectors/peers/packet-happp.c b/admin/wireshark-dissectors/peers/packet-happp.c
index 43babd2..581262f 100644
--- a/admin/wireshark-dissectors/peers/packet-happp.c
+++ b/admin/wireshark-dissectors/peers/packet-happp.c
@@ -214,7 +214,7 @@
 	STD_T_SINT = 0, /* signed int */
 	STD_T_UINT,     /* unsigned int */
 	STD_T_ULL,      /* unsigned long long */
-	STD_T_FRQP,     /* freq_ctr_period structure made of three unsigned int */
+	STD_T_FRQP,     /* freq_ctr structure made of three unsigned int */
 };
 
 /* Prototypes */