It looks like in langdale/master do_start() was stripped of essential functionality [1] 

[1] https://git.yoctoproject.org/poky/tree/meta/recipes-connectivity/connman/connman/connman?h=langdale

In kirkstone this functionality is still there[2]

[2] https://git.yoctoproject.org/poky/tree/meta/recipes-connectivity/connman/connman/connman?h=kirkstone

-->

nfsroot=0

exec 9<&0 < /proc/mounts
while read dev mtpt fstype rest; do
	if test $mtpt = "/" ; then
		case $fstype in
		    nfs | nfs4)
			nfsroot=1
			break
			;;
		    *)
			;;
		esac
	fi
done

do_start() {
	if test $nfsroot -eq 1 ; then
	    NET_DEVS=`cat /proc/net/dev | sed -ne 's/^\([a-zA-Z0-9 ]*\):.*$/\1/p'`
	    NET_ADDR=`cat /proc/cmdline | sed -ne 's/^.*ip=\([^ :]*\).*$/\1/p'`

	    if [ ! -z "$NET_ADDR" ]; then
		if [ "$NET_ADDR" = dhcp ]; then
		    ethn=`ifconfig | grep "^eth" | sed -e "s/\(eth[0-9]\)\(.*\)/\1/"`
		    if [ ! -z "$ethn" ]; then
			EXTRA_PARAM="$EXTRA_PARAM -I $ethn"
		    fi
		else
		    for i in $NET_DEVS; do
			ADDR=`ifconfig $i | sed 's/addr://g' | sed -ne 's/^.*inet \([0-9.]*\) .*$/\1/p'`
			if [ "$NET_ADDR" = "$ADDR" ]; then
			    EXTRA_PARAM="$EXTRA_PARAM -I $i"
			    break
			fi
		    done
		fi
	    fi
	fi
	if [ -f @DATADIR@/connman/wired-setup ] ; then
		. @DATADIR@/connman/wired-setup
	fi
	$DAEMON $EXTRA_PARAM
}

<--

Without this extra checks connman needs to be disabled if you boot with a rootfs over nfs, so I suggest to add it back in.