8170544: Fix code scan findings in libnet
Reviewed-by: goetz, chegar

8167481: cleanup of headers and includes for native libnet
Reviewed-by: chegar

8168405: Pending exceptions in java.base/windows/native
Reviewed-by: chegar, clanger

8167295: Further cleanup to the native parts of libnet/libnio
Reviewed-by: chegar

8166850: No runtime error expected after calling NET_MapSocketOption
Reviewed-by: chegar

8158023: SocketExceptions contain too little information sometimes
Reviewed-by: rriggs, msheppar, chegar

8133249: Occasional SIGSEGV: non thread-safe use of strerr in getLastErrorString
Reviewed-by: igerasim, rriggs, christos

8072466: Deadlock when initializing MulticastSocket and DatagramSocket
Reviewed-by: chegar

7010989: Duplicate closure of file descriptors leads to unexpected and incorrect closure of sockets
Reviewed-by: chegar

8054834: Modular Source Code
Reviewed-by: alanb, chegar, ihse, mduigou
Contributed-by: alan.bateman@oracle.com, alex.buckley@oracle.com, chris.hegarty@oracle.com, erik.joelsson@oracle.com, jonathan.gibbons@oracle.com, karen.kinnear@oracle.com, magnus.ihse.bursie@oracle.com, mandy.chung@oracle.com, mark.reinhold@oracle.com, paul.sandoz@oracle.com