Move doxytags file to html output directory

So that downstream projects can make use of the generated
Doxygen tags file, move it into the html directory that is
transferred to Nexus.

Change-Id: I04dc4777c9ea62f429f783f66ef4e2ecb2923131
Signed-off-by: Chris Luke <chrisy@flirble.org>
diff --git a/doxygen/doxygen.cfg b/doxygen/doxygen.cfg
index 7b24ae8..8844965 100644
--- a/doxygen/doxygen.cfg
+++ b/doxygen/doxygen.cfg
@@ -2106,7 +2106,7 @@
 # tag file that is based on the input files it reads. See section "Linking to
 # external documentation" for more information about the usage of tag files.
 
-GENERATE_TAGFILE       = $(BUILD_ROOT)/docs/vpp.doxytags
+GENERATE_TAGFILE       = $(BUILD_ROOT)/docs/html/vpp.doxytags
 
 # If the ALLEXTERNALS tag is set to YES, all external class will be listed in
 # the class index. If set to NO, only the inherited external classes will be