make install: also install gtpie.h
diff --git a/gtp/Makefile.am b/gtp/Makefile.am
index 4ad9f65..9586dfe 100644
--- a/gtp/Makefile.am
+++ b/gtp/Makefile.am
@@ -1,6 +1,6 @@
 lib_LTLIBRARIES = libgtp.la
 
-include_HEADERS = gtp.h pdp.h
+include_HEADERS = gtp.h pdp.h gtpie.h
 
 AM_CFLAGS = -O2 -fno-builtin -Wall -DSBINDIR='"$(sbindir)"' -ggdb $(LIBOSMOCORE_CFLAGS)