gsm_08_58: add flexible array member to 'struct ipac_preproc_ave_cfg'

Some averaging methods may have additional parameters, so let's
make it easier to access them for the API user.

Change-Id: I2f4ed56837dd479dbbd10c0a7df0ed7565d3946a
Related: SYS#4918
diff --git a/include/osmocom/gsm/protocol/gsm_08_58.h b/include/osmocom/gsm/protocol/gsm_08_58.h
index 046d358..e9c14e6 100644
--- a/include/osmocom/gsm/protocol/gsm_08_58.h
+++ b/include/osmocom/gsm/protocol/gsm_08_58.h
@@ -775,10 +775,12 @@
 		reserved:1;
 	uint8_t h_reqt:5,
 		ave_method:3;
+	uint8_t params[0];
 #elif OSMO_IS_BIG_ENDIAN
 /* auto-generated from the little endian part above (libosmocore/contrib/struct_endianess.py) */
 	uint8_t reserved:1, param_id:2, h_reqave:5;
 	uint8_t ave_method:3, h_reqt:5;
+	uint8_t params[0];
 #endif
 }__attribute__ ((packed));