Add dependency to libosmocodec (part of libosmocore)

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/configure.ac b/configure.ac
index fbddb34..c09b27f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -20,6 +20,7 @@
 AC_PROG_CC
 
 # Checks for libraries.
+PKG_CHECK_MODULES(LIBOSMOCODEC, libosmocodec >= 0.1.25)
 
 # Checks for header files.
 AC_CHECK_HEADERS([stdint.h stdlib.h string.h unistd.h])