systemd-generators: prevent early exit

Turns out that `foo && bar` fails when under `set -e` if `foo` fails.
That's not what I wanted. I have no idea why I haven't just used a
proper `if` statement. Well, I do, now.

Change-Id: Ic40705fbc9c6e48aa81bb1e9d45d4388f1de8eda
diff --git a/board/czechlight/clearfog/overlay/usr/lib/systemd/system-generators/osc b/board/czechlight/clearfog/overlay/usr/lib/systemd/system-generators/osc
index 3c219c3..fe12698 100755
--- a/board/czechlight/clearfog/overlay/usr/lib/systemd/system-generators/osc
+++ b/board/czechlight/clearfog/overlay/usr/lib/systemd/system-generators/osc
@@ -12,16 +12,20 @@
 	ETH3_NAME=oscE
 fi
 
-[[ -n "${ETH2_NAME+set}" ]] && cat > /run/systemd/network/30-eth2.link <<EOF
+if [[ -n "${ETH2_NAME+set}" ]] ; then
+	cat > /run/systemd/network/30-eth2.link <<EOF
 [Match]
 Path=platform-f1034000.ethernet
 [Link]
 Name=${ETH2_NAME}
 EOF
+fi
 
-[[ -n "${ETH3_NAME+set}" ]] && cat > /run/systemd/network/30-eth3.link <<EOF
+if [[ -n "${ETH3_NAME+set}" ]]; then
+	cat > /run/systemd/network/30-eth3.link <<EOF
 [Match]
 Path=platform-soc:pcie-pci-*
 [Link]
 Name=${ETH3_NAME}
 EOF
+fi