Move BSSMAP_MSG_* defines to header file

This will be reused be several tests related to TS 48.008 and TS 29.205
in follow-up commits.

Change-Id: I4d8cc05b8df8e70c1f6257e53ae3acec7901681f

include/osmocom/gsm/gsm0808.h

@@ -29,6 +29,9 @@
 #include <osmocom/gsm/gsm23003.h>
 #include <osmocom/core/utils.h>
 
+#define BSSMAP_MSG_SIZE 512
+#define BSSMAP_MSG_HEADROOM 128
+
 struct sockaddr_storage;
 
 struct msgb;

src/gsm/gsm0808.c

@@ -34,9 +34,6 @@
  *  message generation/encoding.
  */
 
-#define BSSMAP_MSG_SIZE 512
-#define BSSMAP_MSG_HEADROOM 128
-
 /*! Create "Complete L3 Info" for AoIP, legacy implementation.
  * Instead use gsm0808_create_layer3_aoip2(), which is capable of three-digit MNC with leading zeros.
  *  \param[in] msg_l3 msgb containing Layer 3 Message