Tirex-master: keep peerpath of client

In order to send back to correct tileserver(s),
Tirex-master need to remember peer address/path
when recieve command.

This patch preserve peerpath (for unix domain socket)
in source object.

It fix problem that multiple tileservers send
command to tirex, tirex returns result to
most recent tileserver only.

Signed-off-by: Hiroshi Miura <miurahr@linux.com>