bgpd: Fix peer uptime display in milliseconds

bgpd: Fix peer uptime display in milliseconds

For some reason bgp is calculating the peer uptime
in miliseconds incorrectly.  Additionally we have
the peer_uptime function call that should be doing this!
But since we've choosen different names for the json output
we cannot fix it at this point.

uptime contains the number of seconds of uptime here.  Just
multiply by 1k and display that( as peer_uptime does )

Fixes: #1585
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>