MFC r291296, r291297, r291393:

 Allow drivers to specify a maximum TSP length in bytes if they
 are limited in the amount of data they can handle at once.

 Apply this to the netfront driver.

 Spare fields in struct tcpcb and struct ifnet are used to keep
 the structure sizes the same.
MFC r242306, r250365:

 Add logging for socket attach failures in sonewconn() during accept(2).
 Include the pointer to the PCB so it can be attributed to a particular
 application by corresponding it to "netstat -A" output.
MFC r243627, r243638:

 Fix a race on listen socket teardown where while draining the
 accept queues a new socket/connection may be added to the queue
 due to a race on the ACCEPT_LOCK.

 The submitted patch is slightly changed in comments, teardown
 and locking order and extended with KASSERT's.

 Submitted by:	Vijay Singh <vijju.singh-at-gmail-dot-com>
 Found by:	His team.
MFC r242309:

 Fix a couple of soreceive_stream() issues.

 Submitted by:	trociny