fix set never used warnings

fix set never used warnings

(This patch was modified to leave calls to stream_getl() in place, they
are necessary for the stream's internal pointer to advance to the
correct position. -- Denis)

Signed-off-by: Denis Ovsienko <infrastation@yandex.ru>
Fix gcc warnings about varables that are set but never used.

* bgpd/bgp_attr.c
  * cluster_unintern(): ret
  * transit_unintern(): ret
  * bgp_attr_default_intern(): attre
  * bgp_mp_reach_parse(): rd_high, rd_low
* bgpd/bgp_route.c
  * bgp_announce_check_rsclient(): bgp
* bgpd/bgp_zebra.c
  * zebra_read_ipv4(): ifindex
  * zebra_read_ipv6(): ifindex
* bgpd/bgpd.c
  * bgp_config_write_peer(): filter
* lib/distribute.c
  * distribute_list_all(): dist
  * distribute_list(): dist
  * distribute_list_prefix_all(): dist
  * distribute_list_prefix(): dist
* lib/if_rmap.c
  * if_rmap(): if_rmap
* lib/vty.c
  * vty_accept(): vty
* lib/zclient.c
  * zclient_read(): ret
* zebra/irdp_interface.c
  * if_group(): zi
* zebra/rt_netlink.c
  * kernel_read(): ret, sock