uclibc: fix issues with udp.h, missing stdint.h

Fixes:
  http://autobuild.buildroot.net/results/3e4/3e468c7b1be376024422e2f06750571f64f433a2/
  http://autobuild.buildroot.net/results/8c6/8c629a1c5c4a1d78c8bf09a091a332a424a0f757/



Reported-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>