udhcpc: use readlink rather than realpath

The realpath utility requires all paths exist when canonicalizing
symlinks.  If /etc/resolv.conf points to a tmpfs, then it might
not exist initially.  Use `readlink -f` so that we follow all
symlinks that are available.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
platform: use KERNEL_VERSION to simplify uClibc version checking

This makes reading the logic (as well as adding new code) a lot simpler,
and fixes one or two cases that were broken due to incorrect sub-version
tests.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
readlink: uClibc supports automatic allocation too now

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
readlink: note that our -f is really -e

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Merge git://busybox.net/busybox