MULE-7870: Be able to provide socket configuration for the HTTP connector

Added generic configuration elements in the TCP transport.
The use of '[server]SoTimeout' is redundant here, as is [client]SoTimeout.  Also the choice of attribute names doesn't appear to be at all consistent.  Some use 'so' (e.g. soTimeout), some use both 'socket' and 'so' (e.g. socketSoLinger) and some use neither (e.g. keepAlive)