pinfo->pseudo_header can and should be assumed to be non-null by a

pinfo->pseudo_header can and should be assumed to be non-null by a
dissector.  This fixes Coverity CID 238 (as we *were* assuming it was
non-null in one statement, and then only checking it later).

Set pinfo->p2p_dir to one of P2P_DIR_RECV or P2P_DIR_SENT, as it's
supposed to be, not to a Boolean value, and explain the basis on which
it's being set.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@24055 f5534014-38df-0310-8fa8-9805f1628bb7