m/c/m/core: adjust the minimum ESP size

OVMF firmware refuses to boot from a smaller ESP.

This is due to unknown factors. This patch addresses that problem by
adjusting the partition's minimum size to slightly more than FAT's
advertised lower bound of 32MiB.

Change-Id: I1516ce19a162cd8da51e92aa7783c5a48ecfa77f
Reviewed-on: https://review.monogon.dev/c/monogon/+/421
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/cli/metroctl/core/install.go b/metropolis/cli/metroctl/core/install.go
index 35b49ea..f4c6b96 100644
--- a/metropolis/cli/metroctl/core/install.go
+++ b/metropolis/cli/metroctl/core/install.go
@@ -76,9 +76,10 @@
 	// 5% filesystem overhead
 	partitionSizeBytes := (uint64(float32(5*MiB+args.BundleSize+args.InstallerSize+uint64(len(nodeParamsRaw))) * 1.05)) & align1MiBMask
 	// FAT32 has a minimum partition size of 32MiB, so clamp the lower partition
-	// size to that.
-	if partitionSizeBytes < 32*MiB {
-		partitionSizeBytes = 32 * MiB
+	// size to a notch more than that.
+	minimumSize := uint64(33 * MiB)
+	if partitionSizeBytes < minimumSize {
+		partitionSizeBytes = minimumSize
 	}
 	// If creating an image, create it with minimal size, i.e. 1MiB at each
 	// end for partitioning metadata and alignment.