Fix buggy assertion triggered when sendto() runs out of output buffers
Use SO_REUSEPORT on Linux, if supported.
Documentation nits
Use SO_REUSEPORT on the TCP socket, too
Use IP_PMTUDISC_OMIT instead of IP_DONTFRAG if supported
Merge branch 'assert-fix'

* assert-fix:
  Fix buggy assertion triggered when sendto() runs out of output buffers
Merge branch 'doc-nits'

* doc-nits:
  Documentation nits
Merge branch 'reuseport'

* reuseport:
  Use SO_REUSEPORT on the TCP socket, too
  Use SO_REUSEPORT on Linux, if supported.