regression in a micro update! lib/rtorrent 0.6.18

[Greg Troxel <gdt%lexort.com@localhost>]

0.6.18 fails to build on NetBSD 10:

  libtool: compile:  c++ -std=c++20 -DHAVE_CONFIG_H -I. -I../.. -I./.. -I/tmp/work/net/libtorrent/work/.buildlink/include -Dz_off_t=long -I/tmp/work/net/libtorrent/work/.buildlink/include/libxml2 -pthread -O2 -Dz_off_t=long -DNDEBUG -Wall -fvisibility=hidden -MT system/system.lo -MD -MP -MF system/.deps/system.Tpo -c system/system.cc  -fPIC -DPIC -o system/.libs/system.o
  system/system.cc: In function 'const char* torrent::system::sa_family_enum(int)':
  system/system.cc:131:8: error: 'AF_UNSPEC' was not declared in this scope
    131 |   case AF_UNSPEC:
        |        ^~~~~~~~~
  system/system.cc:133:8: error: 'AF_INET' was not declared in this scope
    133 |   case AF_INET:
        |        ^~~~~~~
  system/system.cc:135:8: error: 'AF_INET6' was not declared in this scope
    135 |   case AF_INET6:
        |        ^~~~~~~~
  system/system.cc:137:8: error: 'AF_UNIX' was not declared in this scope
    137 |   case AF_UNIX:
        |        ^~~~~~~
  gmake[3]: *** [Makefile:1050: system/system.lo] Error 1

I've added a patch to just include sys/socket.h, which POSIX says you
have to include for AF_FOO.  It's been about 40 years!

I wonder how this built on other systems, unless some other include
dragged in sys/socket.h implicitly.


Interestingly, 0.6.17 is ok.  So somehow in a micro update they stopped
including sys/socket.h.  A cautionary tale about "micro updates are
safe".  I would not have seen this coming either!