Fix "show ip bgp dampened-paths" garbage output.

Fix "show ip bgp dampened-paths" garbage output.

* bgpd/bgp_damp.c: Make bgp_damp_reuse_time_vty() accept a buffer and
  length, rather than returning a local var buffer whose contents can get
  trounced.  Remove duplicate BGP_UPTIME_LEN define.
* bgpd/bgp_damp.h: bgp_damp_reuse_time_vty() prototype change.
* bgpd/bgp_route.c: Provide bgp_damp_reuse_time_vty() with a buffer and
  length.  Remove duplicate BGP_UPTIME_LEN define.

This problem was noticed in 2005...

  http://hibernia.jakma.org/~paul/patches/quagga-test.diff

...but the fix didn't make it into the code.

Signed-off-by: Chris Caputo <ccaputo@alt.net>