package/dhcpcd: systemv and systemd services conflict with NetworkManager

When NetworkManager and dhcpcd packages are both enabled, dhcpcd
services and NetworkManager both spawn dhcpcd. This causes the network
port to retrieve an IP address and later lose it a few seconds after
startup.

This patch prevents dhcpcd services from launching dhcpcd if
NetworkManager is enabled.

Signed-off-by: Jim Brennan <jbrennan@impinj.com>
[Thomas: add a comment in the code to explain the seemingly strange
condition.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/dhcpcd/dhcpcd.mk

@@ -36,6 +36,10 @@ define DHCPCD_INSTALL_TARGET_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) install DESTDIR=$(TARGET_DIR)
 endef
 
+# When network-manager is enabled together with dhcpcd, it will use
+# dhcpcd as a DHCP client, and will be in charge of running, so we
+# don't want the init script or service file to be installed.
+ifeq ($(BR2_PACKAGE_NETWORK_MANAGER),)
 define DHCPCD_INSTALL_INIT_SYSV
 	$(INSTALL) -m 755 -D package/dhcpcd/S41dhcpcd \
 		$(TARGET_DIR)/etc/init.d/S41dhcpcd
@@ -48,6 +52,7 @@ define DHCPCD_INSTALL_INIT_SYSTEMD
 	ln -sf ../../../../usr/lib/systemd/system/dhcpcd.service \
 		$(TARGET_DIR)/etc/systemd/system/multi-user.target.wants/dhcpcd.service
 endef
+endif
 
 # NOTE: Even though this package has a configure script, it is not generated
 # using the autotools, so we have to use the generic package infrastructure.