libiptc: make library available as a shared library

Tested-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/include/Makefile.am b/include/Makefile.am
index 6206bd2..0a1abea 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -6,3 +6,7 @@
 if ENABLE_LIBIPQ
 include_HEADERS += libipq/libipq.h
 endif
+
+nobase_include_HEADERS += \
+	libiptc/ipt_kernel_headers.h libiptc/libiptc.h \
+	libiptc/libip6tc.h libiptc/libxtc.h