package/pppd: add linux-pam optional dependency

linux-pam is an optional dependency which is enbled by default since
bump to version 2.5.0 in commit 0c15169f5ae57d88a77df34cc896044a37c9597b
and
https://github.com/ppp-project/ppp/commit/2883dd07101bf851e2ea368f0c04c91aea85cff2

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/pppd/pppd.mk

@@ -17,6 +17,13 @@ PPPD_AUTORECONF = YES
 PPPD_INSTALL_STAGING = YES
 PPPD_CONF_OPTS = --enable-multilink
 
+ifeq ($(BR2_PACKAGE_LINUX_PAM),y)
+PPPD_CONF_OPTS += --with-pam=$(STAGING_DIR)/usr
+PPPD_DEPENDENCIES += linux-pam
+else
+PPPD_CONF_OPTS += --without-pam
+endif
+
 ifeq ($(BR2_PACKAGE_OPENSSL),y)
 PPPD_CONF_OPTS += \
 	--enable-eaptls \