Did you mean something like that?
(gdb) bt
#0 0x00007ffff4fef18d in nanosleep () at
../sysdeps/unix/syscall-template.S:81
#1 0x00007ffff526ef88 in g_usleep () from
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00000000004c64d5 in nm_utils_kill_process_sync (pid=17000,
start_time=<optimized out>, sig=9, log_domain=192, log_name=0x5316dc
"dhcp-client",
wait_before_kill_msec=500, sleep_duration_msec=50) at
NetworkManagerUtils.c:803
#3 0x000000000045d9bb in nm_dhcp_client_stop_existing (pid_file=0x864c30
"/var/run/dhclient-wwan0.pid", binary_name=0x804030 "dhclient")
at dhcp-manager/nm-dhcp-client.c:606
#4 0x000000000043f8b2 in dhclient_start (client=0x7fffffffda90,
mode_opt=0x7fffffffdaa0 "", duid=0x0, release=0,
out_pid=0x7ffff4fdaf00 <default_overflow_region+32>) at
dhcp-manager/nm-dhcp-dhclient.c:355
#5 0x00000000004402c5 in ip4_start (client=0x84f590,
dhcp_anycast_addr=0x0, last_ip4_address=0x0) at
dhcp-manager/nm-dhcp-dhclient.c:498
#6 0x00000000004614fb in client_start (self=self@entry=0x7e8a20,
iface=iface@entry=0x81c370 "wwan0", ifindex=ifindex@entry=9,
hwaddr=hwaddr@entry=0x856180, uuid=uuid@entry=0x81d340
"4ee0469b-3bf5-45f9-9c42-3c9b5d531eaf", priority=priority@entry=450,
ipv6=0,
dhcp_client_id=0x0, timeout=15, dhcp_anycast_addr=0x0,
hostname=0x844a60 "ente", info_only=0,
privacy=NM_SETTING_IP6_CONFIG_PRIVACY_DISABLED,
last_ip4_address=0x0) at dhcp-manager/nm-dhcp-manager.c:268
#7 0x0000000000461744 in nm_dhcp_manager_start_ip4 (self=0x7e8a20,
iface=iface@entry=0x81c370 "wwan0", ifindex=ifindex@entry=9,
hwaddr=hwaddr@entry=0x856180, uuid=uuid@entry=0x81d340
"4ee0469b-3bf5-45f9-9c42-3c9b5d531eaf", priority=priority@entry=450,
send_hostname=1,
dhcp_hostname=0x844a60 "ente", dhcp_client_id=0x0, timeout=15,
dhcp_anycast_addr=0x0, last_ip_address=0x0) at
dhcp-manager/nm-dhcp-manager.c:308
#8 0x000000000044f357 in dhcp4_start (self=0x87a7b0, connection=<optimized
out>, reason=0x7fffffffdfec) at devices/nm-device.c:3154
#9 0x000000000044f68e in act_stage3_ip4_config_start (self=0x87a7b0,
out_config=0x0, reason=0x7fffffffdfec) at devices/nm-device.c:3426
---Type <return> to continue, or q <return> to quit---
#10 0x0000000000456cc0 in nm_device_activate_stage3_ip4_start
(self=0x87a7b0) at devices/nm-device.c:4616
#11 0x00000000004588e8 in nm_device_activate_stage3_ip_config_start
(user_data=0x87a7b0) at devices/nm-device.c:4765
#12 0x00007ffff5246b4d in g_main_context_dispatch () from
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#13 0x00007ffff5246f20 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#14 0x00007ffff5247242 in g_main_loop_run () from
/lib/x86_64-linux-gnu/libglib-2.0.so.0
#15 0x0000000000432e4e in main (argc=1, argv=0x7fffffffe2e8) at main.c:502
