general: remove inline qualifiers and move in-header functions to objects

* (general) Move functions in headers into files, to be compiled into
  shared object files. Remove inline qualifier from functions. Let the
  compiler do the work.
diff --git a/bgpd/bgpd.c b/bgpd/bgpd.c
index a75fb93..5dc014b 100644
--- a/bgpd/bgpd.c
+++ b/bgpd/bgpd.c
@@ -695,7 +695,7 @@
     }
 }
 
-static inline void
+static void
 peer_free (struct peer *peer)
 {
   assert (peer->status == Deleted);