profiles: re-add udev to default USE flags

Reapply 943574b4, build_packages can handle the circular dependency that
this introduces between systemd and util-linux now.
profiles: do not disable perl's gdbm use flag

It appears turning off this flag does not actually prevent perl from
trying to build against gdbm. Enable the flag so dependencies are
consistent with perl's actual behavior.
iproute2: restore two mistakenly deleted patches

Commit 3d5e4758 pruned a little too deeply.
coreos-init: update with some minor fixes

- Removes ld.so.cache generator, systemd 215 does this.
- Fix udev rule for GCE compatibility.
systemd: fix build dependencies for man pages
Merge pull request #755 from marineam/dev

Misc updates/fixes