Allow compile with -std=c23

[heitbaum]

• Fixes Build fails with gcc-15 / std=c23 #134

When compiling with -std=c23 the following errors are observed.

common/qtypes.h:37:15: error: cannot use keyword 'false' as enumeration constant
   37 | typedef enum{ false, true, ENSURE_INT_QBOOL = 0x70000000 } qboolean;
      |               ^~~~~
common/qtypes.h:37:23: error: cannot use keyword 'true' as enumeration constant
   37 | typedef enum{ false, true, ENSURE_INT_QBOOL = 0x70000000 } qboolean;
      |                       ^~~~

common/net_main.c:869:9: error: too many arguments to function 'pp->procedure'; expected 0, have 1
  869 |         pp->procedure(pp->arg);
      |         ^~            ~~~~~~~
common/net.h:320:12: note: declared here
  320 |     void (*procedure) ();
      |            ^~~~~~~~~

common/net_main.c:112:56: error: initialization of 'void (*)(void *)' from incompatible pointer type 'void (*)(void)' [-Wincompatible-pointer-types]
  112 | static PollProcedure slistSendProcedure = { NULL, 0.0, Slist_Send };
      |                                                        ^~~~~~~~~~
common/net_main.c:113:56: error: initialization of 'void (*)(void *)' from incompatible pointer type 'void (*)(void)' [-Wincompatible-pointer-types]
  113 | static PollProcedure slistPollProcedure = { NULL, 0.0, Slist_Poll };
      |                                                        ^~~~~~~~~~
common/net_dgrm.c:512:8: error: initialization of 'void (*)(void *)' from incompatible pointer type 'void (*)(struct test_poll_state *)' [-Wincompatible-pointer-types]
  512 |        Test_Poll,
      |        ^~~~~~~~~
common/net_dgrm.c:647:7: error: initialization of 'void (*)(void *)' from incompatible pointer type 'void (*)(struct test_poll_state *)' [-Wincompatible-pointer-types]
  647 |       Test2_Poll,
      |       ^~~~~~~~~~

Fix:

• update enum as false0 and true1 as the enum are already 0 and 1, and map to false/true
• Update the function declarations to pass (void *) as procedure