coverity: build osmo-hnbgw with '--enable-pfcp'

This should improve the analysis depth for osmo-hnbgw.

Change-Id: I33b44a1c2ffde80b000b41b78569ff2f55bc98ed
diff --git a/coverity/build_Osmocom.sh b/coverity/build_Osmocom.sh
index 3bf9d4b..61bd2b7 100755
--- a/coverity/build_Osmocom.sh
+++ b/coverity/build_Osmocom.sh
@@ -103,7 +103,8 @@
 build_default osmo-smlc
 build_default osmo-cbc
 build_default osmo-hnodeb
-build_default osmo-hnbgw
+build_default osmo-hnbgw \
+	--enable-pfcp
 build_default osmo-bsc-nat
 
 # GMR