add external/kmod

The depmod utility, which is part of kmod, is required to generate
dependencies between Linux kernel modules.
Bug: 35413697
Change-Id: I79afa00c6e8cbb98ad91ee6dd9ca2aad32b2ce03

default.xml

@@ -185,6 +185,7 @@
   <project path="external/junit" name="platform/external/junit" groups="pdk" />
   <project path="external/junit-params" name="platform/external/junit-params" groups="pdk" />
   <project path="external/kernel-headers" name="platform/external/kernel-headers" groups="pdk" />
+  <project path="external/kmod" name="platform/external/kmod" groups="pdk" />
   <project path="external/ksoap2" name="platform/external/ksoap2" groups="pdk" />
   <project path="external/libavc" name="platform/external/libavc" groups="pdk" />
   <project path="external/libbrillo" name="platform/external/libbrillo" groups="pdk" />