NetBpfLoad: hacky way to make LPM_TRIE bpf maps work.

Longer term we should fix the bpf_map_def.h to
actually set map_flags correctly.

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I4e7954ccd0afad4ca8d9cec179ad6efa20592609
diff --git a/bpf/loader/NetBpfLoad.cpp b/bpf/loader/NetBpfLoad.cpp
index 59712b1..32b506d 100644
--- a/bpf/loader/NetBpfLoad.cpp
+++ b/bpf/loader/NetBpfLoad.cpp
@@ -604,6 +604,9 @@
     if (type == BPF_MAP_TYPE_DEVMAP || type == BPF_MAP_TYPE_DEVMAP_HASH)
         desired_map_flags |= BPF_F_RDONLY_PROG;
 
+    if (type == BPF_MAP_TYPE_LPM_TRIE)
+        desired_map_flags |= BPF_F_NO_PREALLOC;
+
     // The .h file enforces that this is a power of two, and page size will
     // also always be a power of two, so this logic is actually enough to
     // force it to be a multiple of the page size, as required by the kernel.
@@ -779,7 +782,7 @@
               .key_size = md[i].key_size,
               .value_size = md[i].value_size,
               .max_entries = max_entries,
-              .map_flags = md[i].map_flags,
+              .map_flags = md[i].map_flags | (type == BPF_MAP_TYPE_LPM_TRIE ? BPF_F_NO_PREALLOC : 0),
             };
             if (isAtLeastKernelVersion(4, 15, 0))
                 strlcpy(req.map_name, mapNames[i].c_str(), sizeof(req.map_name));