adb: HACK: (linux only) allow temp mitigation for multithreaded issues

There are serious multithreading issues between the fdevent and transport
subsystems which both manipulate struct asocket and struct fde concurrently.
The prevalent symptom being around multiple socket closures which stomp
 on each other, typically causing:
   "glibc detected *** adb: double free or corruption ..."

This HACK allows forcing CPU affinity via an env var. E.g.:
  export ADB_CPU_AFFINITY_BUG6558362=0
which will cause ONLY the adb server and all its threads to be pegged
to CPU 0.

The result is visible in valgrind's helgrind: no *socket_close() related
data races. But tons of other races are still there.

Bug: 6558362
Change-Id: I0f112390a6a921c64b2a783297be9e99ce27fd56