Makefile.am: Make libraries depend on .map files

Without this, an update to the .map file doesn't re-trigger a re-link of
the library.

Change-Id: If0ea6f41730a28b04562d45efa6ca376abaf3f6b
diff --git a/src/isdn/Makefile.am b/src/isdn/Makefile.am
index 97e7a28..2aed0bf 100644
--- a/src/isdn/Makefile.am
+++ b/src/isdn/Makefile.am
@@ -23,3 +23,4 @@
 libosmoisdn_la_LIBADD = libisdnint.la $(TALLOC_LIBS)
 
 EXTRA_DIST = libosmoisdn.map
+EXTRA_libosmoisdn_la_DEPENDENCIES = libosmoisdn.map