Currently, the dump methods open BpfMap objects and never close
them. This leaks filedescriptors, and if dump is called often
enough, will crash the networkstack process.
Fix this by using try-with-resources statements that
automatically close the map when exiting the try block.
Change the signature of BpfMap#close from "throws Exception" to
"throws ErrnoException" since it does not throw any other type
of checked exceptions.
Test: "lsof | grep network_st" while running "dumpsys tethering bpf" in a loop
Change-Id: I66c407454c2715bf41bf3a2e81bd582f9ea5a905
555472a186