CBIDXT-16: packet framing sub-package.

carved out dataport packet framing into `transport` sub-package.
will be used by `queryport` as well.

Change-Id: I6108a93cdf23118f0ed37ac153e9400b2bad4508
Reviewed-on: http://review.couchbase.org/41174
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>