Add _buf() functions to bypass static string buffers

We have a number of static buffers in use in libosmo*.  This means
the related functions are not usable in a thread-safe way.  While
we so far don't have many multi-threaded programs in the osmocom
universe, the static buffers also prevent us from calling the same
e.g. string-ify function twice within a single printf() call.

Let's make sure there's an alternative function in all those cases,
where the user can pass in a caller-allocated buffer + size, and make
the 'classic' function with the static buffer a wrapper around that
_buf() variant.

Change-Id: Ibf85f79e93244f53b2684ff6f1095c5b41203e05
diff --git a/src/gb/libosmogb.map b/src/gb/libosmogb.map
index 2ad3ff7..21929da 100644
--- a/src/gb/libosmogb.map
+++ b/src/gb/libosmogb.map
@@ -64,6 +64,7 @@
 gprs_ns_tx_unblock;
 gprs_ns_vty_init;
 gprs_ns_ll_str;
+gprs_ns_ll_str_buf;
 gprs_ns_ll_copy;
 gprs_ns_ll_clear;
 gprs_ns_msgb_alloc;