Merge topic branch t/net into master

A moderately sized series which contains a bunch of simple cleanups
for net.c and net.h.

* refs/heads/t/net:
  net: De-doxify static functions.
  net: Refer to correct man page in stringify_port().
  net: Pass true/false instead of 0/1 to makesock().
  net: Demote log level of error message in makesock().
  net: Rename para_connect_simple() -> para_connect().
  net: Make is_valid_ipv{4,6}_address() local to net.c.
  net: Remove IPPROTO_DCCP define.
  net: Make single-use macros local.
  net: Combine documentation of struct flowopts.
  net: Drop extern keyword of function declarations.

diff --cc NEWS.md
index 5a00175c3255702b03ec86e0af1938863f53ba4d,5a00175c3255702b03ec86e0af1938863f53ba4d..c21cc858ef2c4ab5030a4f1e8996921dd9585513
--- 1/NEWS.md
--- 2/NEWS.md
+++ b/NEWS.md
@@@ -1,6 -1,6 +1,15 @@@
  NEWS
  ====
  
++------------------------------------------
++0.7.2 (to be announced) "optical friction"
++------------------------------------------
++
++- Minor cleanup of the net subsystem.
++
++Downloads:
++[tarball](./releases/paraslash-git.tar.xz)
++
  --------------------------------------
  0.7.1 (2022-10-03) "digital spindrift"
  --------------------------------------
@@@ -27,6 -27,6 +36,7 @@@ usual mix of bug fixes and minor improv
    requires support from the compiler, the oldest supported gcc version
    has been bumped to gcc-5.4 (released in 2015).
  
++Downloads:
  [tarball](./releases/paraslash-0.7.1.tar.xz),
  [signature](./releases/paraslash-0.7.1.tar.xz.asc)
  

diff --cc client_common.c
Simple merge