The mountmsdosfs() function had an insane sanity test, remove it.

Trying FAT32 on a small partition failed to mount because
pmp->pm_Sectors was nonzero.  Normally, FAT32 file systems are so
large that the 16-bit pm_Sectors can't hold the size.  This is
indicated by setting it to 0 and using only pm_HugeSectors.  But at
least old versions of newfs_msdos use the 16-bit field if possible,
and msdosfs supports this except for breaking its own support in the
sanity check.  This is quite different from the handling of pm_FATsecs
-- now the 16-bit value is always ignored for FAT32 except for
checking that it is 0, and newfs_msdos doesn't use the 16-bit value
for FAT32.

Submitted by:	bde
MFC after:	1 week

sys/fs/msdosfs/msdosfs_vfsops.c

@@ -553,8 +553,7 @@ mountmsdosfs(struct vnode *devvp, struct mount *mp)
 	}
 
 	if (pmp->pm_RootDirEnts == 0) {
-		if (pmp->pm_Sectors
-		    || pmp->pm_FATsecs
+		if (pmp->pm_FATsecs
 		    || getushort(b710->bpbFSVers)) {
 			error = EINVAL;
 #ifdef MSDOSFS_DEBUG