udp_sendspace, to avoid a situation where jumbograms (datagrams > 9KB)
are unnecessarily fragmented.
A common use case for this is OSPF link-state database synchronization
during adjacency bringup on a high speed network with a large MTU.
It is not possible to auto-tune this setting until a socket is bound to
a given interface, and because the laddr part of the inpcb tuple may be
overridden, it makes no sense to do so. Applications may request a larger
socket buffer size by using the SO_SENDBUF and SO_RECVBUF socket options.
Certain applications such as Quagga ospfd do not probe for interface MTU
and therefore do not increase SO_SENDBUF in this use case.
XORP is not affected by this problem as it preemptively uses SO_SENDBUF
and SO_RECVBUF to account for any possible additional latency in XRL IPC.
PR: kern/108375
Requested by: Vladimir Ivanov
MFC after: 1 week
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