server: Use local inbound var in version handler.
server: Use local inbound var in version handler.

This modifies the OnVersion handler for server peers to use a local
variable for the inbound status of the peer in order to avoid grabbing
the mutex multiple times.

While here, it also does some light cleanup.  There are no functional
changes.

jrick/dcrd,decred/dcrd,jrick/dcrd,decred/dcrd