Bug 4309: Fix the presence of extensions detection in SSL Hello messages

Bug 4309: Fix the presence of extensions detection in SSL Hello messages

RFC5246 section 7.4.1.3 (Server Hello) says:

   The presence of extensions can be detected by determining whether
   there are bytes following the compression_method field at the end
   of the ServerHello.

Current parsing Hello code checks whether there are bytes in the whole
SSL message. It does not account for the fact that the message may
contain more than just ServerHello.

This patch fixes this issue and tries to improve the related code to
avoid related problems in the future.

This is a Measurement Factory project