uclibc: fix networking support on sparc

While updating the default config for Sparc, I noticed that networking
is broken. The reason is a uClibc backport patch from uClibc
master. This commit adds a fix on top of it, which was submitted to
upstream uClibc.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>