[doc] Doxygen documentation on osmo_hexdump print buffer size

Change-Id: I83ca2a3a555e5b3c1b7f23bf9e463a5063a8006c
diff --git a/src/utils.c b/src/utils.c
index b4345c7..534916b 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -235,6 +235,9 @@
  *
  * This function will print a sequence of bytes as hexadecimal numbers,
  * adding one space character between each byte (e.g. "1a ef d9")
+ *
+ * The maximum size of the output buffer is 4096 bytes, i.e. the maximum
+ * number of input bytes that can be printed in one call is 1365!
  */
 char *osmo_hexdump(const unsigned char *buf, int len)
 {
@@ -248,6 +251,9 @@
  *
  * This function will print a sequence of bytes as hexadecimal numbers,
  * without any space character between each byte (e.g. "1aefd9")
+ *
+ * The maximum size of the output buffer is 4096 bytes, i.e. the maximum
+ * number of input bytes that can be printed in one call is 2048!
  */
 char *osmo_hexdump_nospc(const unsigned char *buf, int len)
 {