8196956: (ch) More channels cleanup

[Pavel Rappo]

Looks good.

> On 7 Feb 2018, at 14:45, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> 
> 
> This is a further small patch to the network channels in advance of more complicated changes to split the blocking/non-blocking code paths. The changes in this patch are very simple and amount to:
> 
> - AbstractSelectableChannel::isBlocking changed to not block on regLock
> - the ServerSocketChannel socket adaptors now consistently checks the blocking mode
> - fix DatagramChannelImpl constructor to consistency track the the UDP socket usage
> 
> The webrev is here:
>   http://cr.openjdk.java.net/~alanb/8196956/webrev/index.html
> 
> (ignore the change to make/autoconf/lib-bundled.m4 in the patch, this is to workaround temporary build breakage with build changes pushed to jdk/jdk yesterday).
> 
> -Alan