sys/gnu/vfs/ext2fs: Remove|fix duplicated macro definitions
- Define MAXNAMLEN using EXT2_NAME_LEN since EXT2_NAME_LEN
is the original ondisk definition.
- Bring back MAXSYMLINKLEN that was removed in a0403c0
using EXT2_MAXSYMLINKLEN. It's probably better to keep both
EXT2_MAXSYMLINKLEN and MAXSYMLINKLEN just like above MAXNAMLEN
does considering it's been exposed to userspace and removing
may break them (although there are probably none or very few).
- Remove duplicated MAXMNTLEN definition.
- (Note that dfly's ext2 seems to be broken currently)