dhcpcd needs 12 seconds to boot

Because I want to re-purpose my my Banana Pi, I switched to an old Raspberry Pi 1 as UPnP renderer for the stereo system in the living room. ​

Since most of the day the power strip is switched off, I wanted the Raspberry Pi to boot as fast as possible - so that we don't have to wait for too long to be able to use it after powering on. ​

I used systemd-analyze to check what slows down the boot, and saw: ​

$ systemd-analyze
Startup finished in 3.143s (kernel) + 1min 31.686s (userspace) = 1min 34.830s

$ systemd-analyze blame
         12.246s dhcpcd.service
          6.185s dev-mmcblk0p2.device
          3.501s networking.service
             ...​

At first I switched from DHCP to a static IP by adding the following to /etc/dhcpcd.conf: ​

interface enxb827eb9e8acf
static ip_address=192.168.3.36/24
static routers=192.168.3.3
static domain_name_servers=192.168.3.3

(The network interface name can be found with ifconfig.) ​

After rebooting I saw that the dhcpcd startup had dropped from 12 seconds to 7! But that's still too long for static network configuration. ​

The log told me why the DHCP client daemon took so long: ​

$ journalctl
...
Jan 20 22:26:44 raspistereo dhcpcd[256]: enxb827eb9e8acf: carrier acquired
Jan 20 22:26:44 raspistereo dhcpcd[256]: enxb827eb9e8acf: probing address 192.168.3.36/24
Jan 20 22:26:49 raspistereo dhcpcd[256]: enxb827eb9e8acf: using static address 192.168.3.36/24
...​

It spent 5 seconds checking if someone else in the network is using the same IP address. That's something I do not need, so I disabled it in /etc/dhcpcd.conf, together with IPv6 that I don't need in my internal network: ​

noarp
ipv4only
noipv6

Rebooting and ... 2.2 seconds for dhcpcd. That's 10 seconds faster now. gmediarenderer is available after 16 seconds now: ​

$ systemd-analyze critical-chain gmrender.service
gmrender.service +1.527s
└─sound.target @14.714s​

(I'd like to have 2-3 seconds boot time, but the current state is acceptable.) ​