MEDIUM: stick-tables: Add GPT0 in the stick tables

This patch adds GPT0 (General Purpose Tag 0). It is useful for storing
a simple state.
diff --git a/src/stick_table.c b/src/stick_table.c
index 9c053bc..5e7a2c4 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -584,6 +584,7 @@
  */
 struct stktable_data_type stktable_data_types[STKTABLE_DATA_TYPES] = {
 	[STKTABLE_DT_SERVER_ID]     = { .name = "server_id",      .std_type = STD_T_SINT  },
+	[STKTABLE_DT_GPT0]          = { .name = "gpt0",           .std_type = STD_T_UINT  },
 	[STKTABLE_DT_GPC0]          = { .name = "gpc0",           .std_type = STD_T_UINT  },
 	[STKTABLE_DT_GPC0_RATE]     = { .name = "gpc0_rate",      .std_type = STD_T_FRQP, .arg_type = ARG_T_DELAY  },
 	[STKTABLE_DT_CONN_CNT]      = { .name = "conn_cnt",       .std_type = STD_T_UINT  },