fix "-Werror" build against latest libosmo-abis

libosmo-abisrecently marked the 'out_cb' of the subchan_demux
as 'const', which caused compiler warnings/errors.

Related: libosmo-abis.git Ia082b9fddf03d02afd007825a1588a3ef0dbedae
Change-Id: I0cf430980e50fa8094f0efc7642004fb5923c4c6
diff --git a/src/e1cap_dump.c b/src/e1cap_dump.c
index bcb4916..4cc8538 100644
--- a/src/e1cap_dump.c
+++ b/src/e1cap_dump.c
@@ -153,11 +153,12 @@
 }
 
 
-static void handle_data(struct osmo_e1cap_pkthdr *pkt, uint8_t *data, int len)
+static void handle_data(struct osmo_e1cap_pkthdr *pkt, const uint8_t *idata, int len)
 {
+	uint8_t data[len];
 	struct timeval tv;
 
-	flip_buf_bits(data, len);
+	flip_buf_bits(data, idata, len);
 #if 0
 	/* filter out all-ff/all-fe/all-7f */
 	if (all_bytes_are(0xff, data, len) ||
@@ -193,7 +194,7 @@
 	}
 }
 
-static int subch_demux_out_cb(struct subch_demux *dmx, int ch, uint8_t *data,
+static int subch_demux_out_cb(struct subch_demux *dmx, int ch, const ubit_t *data,
 			      int len, void *c)
 {
 	OSMO_ASSERT(ch == g_filter_subslot);