do not reuse connection if share marked as isolated

"SHAREFLAG_ISOLATED_TRANSPORT" indicates that we should not reuse the socket
for this share (for future mounts).  Mark the socket as server->nosharesock if
share flags returned include SHAREFLAG_ISOLATED_TRANSPORT.

See MS-SMB2 MS-SMB2 2.2.10 and 3.2.5.5

Signed-off-by: Steve French <stfrench@microsoft.com>