Merge changes I181a490b,Ie2619949,I4bd5fbdf,Ifc0c5baa,I437e6607 into main

* changes:
  Use /proc/self instead of calling Os.getPid().
  Use SingleWriterBpfMap in BpfNetMaps.
  Add a microbenchmark test for BpfMap.
  Add a SingleWriterBpfMap class that caches reads.
  Deflake BpfMapTest#testNoFdLeaks.