3rd party module compatibility broken

[michaelortmann]

#1585 changed struct memberlist:

https://github.com/eggheads/eggdrop/pull/1585/files#diff-57a16b1aab40a51784d03f39a2da18c09b36c8c6cefe8b506ad275b77a8a07b9L53

modules like stats.mod use memberlist->user:

https://github.com/michaelortmann/stats.mod/blob/c0e2646260ab93d2fb9b1d1d4d86880d10ed3347/egg_chancontrol.c#L44

and wont compile anymore:

gcc -fPIC -g -O2 -pipe -Wall -I. -I../../.. -I../../.. -I../../../src/mod  -DHAVE_CONFIG_H -I/usr/include -g3 -DDEBUG -DDEBUG_ASSERT -DDEBUG_MEM -DDEBUG_DNS  -DMAKING_MODS -c stats.c
In file included from core/core.c:95,
                 from stats.c:89:
./core/templates_stats_commands.c: In function ‘template_send_hosts’:
./core/templates_stats_commands.c:543:11: warning: the comparison will always evaluate as ‘true’ for the pointer operand in ‘host + -1’ must not be NULL [-Waddress]
  543 |     if (!((host - 1) && host)) {
      |           ^
In file included from stats.c:101:
egg_chancontrol.c: In function ‘egg_check_chan_desynch’:
egg_chancontrol.c:44:73: error: ‘memberlist’ {aka ‘struct memstruct’} has no member named ‘user’
   44 |                                 schan_join(chan, m->nick, m->userhost, m->user ? m->user->handle : NULL);
      |                                                                         ^~
egg_chancontrol.c:44:83: error: ‘memberlist’ {aka ‘struct memstruct’} has no member named ‘user’
   44 |                                 schan_join(chan, m->nick, m->userhost, m->user ? m->user->handle : NULL);
      |                                                                                   ^~
make[2]: *** [Makefile:20: ../stats.o] Error 1
make[2]: Leaving directory '/home/michael/projects/eggdrop/src/mod/stats.mod'
make[1]: *** [Makefile:60: stats.mod_so] Error 2
make[1]: Leaving directory '/home/michael/projects/eggdrop/src/mod'
make: *** [Makefile:251: debug] Error 2

We need to document that breakage and suggest migrating m->user to get_user_from_member(m) in any 3rd party module (or alternatively revert / change the compatibility back)