port/linux: make non-block shutdown read descriptor

the iotivity-lite hangs in read of shutdown descriptor.
so this fix it.
4 jobs for fixShutdown in 3 minutes and 19 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #4510
Android_build

00:02:58

passed #4511
doxygen

00:00:52

passed #4508
Linux_Secured_Test

00:03:19

passed #4509
Linux_Unsecured_Test

00:02:57