nacc: Introduce helper function nacc_fsm_exp_ctrl_ack()

Move FSM internal state checks to its own file. Re-use the helper
function in the 2 places where same stuff is checked.

Change-Id: I9ded6e1c80e6cd7bcf6883bc2e853b6dafb33f7c
diff --git a/src/nacc_fsm.c b/src/nacc_fsm.c
index df38927..ba7bbb7 100644
--- a/src/nacc_fsm.c
+++ b/src/nacc_fsm.c
@@ -895,3 +895,10 @@
 		return false;
 	return !osmo_cgi_ps_cmp(&ctx->cgi_ps, cgi_ps);
 }
+
+bool nacc_fsm_exp_ctrl_ack(const struct nacc_fsm_ctx *ctx, uint32_t fn, uint8_t ts)
+{
+	return ctx->fi->state == NACC_ST_WAIT_CELL_CHG_CONTINUE_ACK &&
+	       ctx->continue_poll_fn == fn &&
+	       ctx->continue_poll_ts == ts;
+}