[rpc] modernize code a bit

Since I'm updating the code in src/kudurpc/connection.{h,cc} and
src/kudu/util/net/socket.{h,cc} in follow-up changelists, I went ahead
and updated the code to be style-compliant, modernized it, and did
other unsorted improvements before introducing the new functionality.

Change-Id: I2634591426c3e107e4d11b661ff62e5cde8a7570
Reviewed-on: http://gerrit.cloudera.org:8080/20815
Tested-by: Alexey Serbin <alexey@apache.org>
Reviewed-by: Mahesh Reddy <mreddy@cloudera.com>
Reviewed-by: Abhishek Chennaka <achennaka@cloudera.com>
9 files changed