bgpd: remove useless control checks about TCP connection

bgpd: remove useless control checks about TCP connection

When attempting to get the src and destination addresses of a given
connection, the API may return the NULL pointer, but further code
in bgp_zebra_nexthop_set() already does a check about the given
pointer.

Relaxing the error code for all the returned adressing.

Fixes: 1ff9a340588a ("bgpd: bgpd-fsm-fix.patch")
Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
(cherry picked from commit ba7130309954fbe8d58854339ca43259149e603a)