bgpd: increase TCP socket buffer size

bgpd: increase TCP socket buffer size

BGP does not respond fairly in high scale.  As the number of BGP peers
and prefixes increase, triggers like interface flaps which lead to BGP
peer flaps, cause blockage in bgp_write.

BGP does handle the cases of TCP socket buffer full by queuing a write
event back, there is no functional issue there as such. Still,
increasing the peer socket buffer size should help reduce event queueing
in BGP.

Signed-off-by: Vipin Kumar <vipin@cumulusnetworks.com>
Reviewed-by: Pradosh Mohapatra <pmohapat@cumulusnetworks.com>
Reviewed-by: Dinesh Dutt <ddutt@cumulusnetworks.com>
[DL: patch split, this is item 3.]
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>