linux/atm_zatm.h was removed in >=linux-headers-5.19. As the hardware is
said to be unlikely working on modern systems, just disable its utility
program to keep the rest building.

See: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=052e1f01bfae8be6

--- a/src/maint/Makefile.am
+++ b/src/maint/Makefile.am
@@ -1,5 +1,5 @@
 BOOTPGMS=atmaddr esi
-SYSPGMS=atmloop atmtcp enitune zntune hediag # nstune
+SYSPGMS=atmloop atmtcp enitune hediag # nstune zntune
 USRPGMS=atmdiag atmdump sonetdiag saaldump
 
 INCLUDES=-I$(srcdir)/../q2931 -I$(srcdir)/../saal -I.
@@ -14,7 +14,7 @@ esi_SOURCES = esi.c
 atmloop_SOURCES = atmloop.c
 atmtcp_SOURCES = atmtcp.c
 enitune_SOURCES = enitune.c
-zntune_SOURCES = zntune.c
+#zntune_SOURCES = zntune.c
 #nstune_SOURCES = nstune.c
 
 atmdiag_SOURCES = atmdiag.c