Doxygen: skip submodules

See-Also: https://gerrit.cesnet.cz/696
Change-Id: I59f75ab50592c1b025f919e3f99171c98e1ccf78
diff --git a/Doxyfile.in b/Doxyfile.in
index dbdefab..250edfb 100644
--- a/Doxyfile.in
+++ b/Doxyfile.in
@@ -4,5 +4,6 @@
 INPUT = @doxy_main_page@ @PROJECT_SOURCE_DIR@ @PROJECT_BINARY_DIR@
 FILE_PATTERNS = *.h *.cpp *.md *.cmake *.yang
 RECURSIVE = YES
+EXCLUDE = @PROJECT_SOURCE_DIR@/submodules/
 EXTRACT_ANON_NSPACES = YES
 USE_MDFILE_AS_MAINPAGE = index.md