fbcode_builder: getdeps: fboss: add libnl manifest

Summary:
This is towards getting open source FBOSS to build using fbcode_builder.
libnl is one of the dependencies for FBOSS. This patch adds a manifest
file to build libnl.

Reviewed By: wez

Differential Revision: D15686853

fbshipit-source-id: f7549df6dc1005630193b024be6e1ea330cc6646

build/fbcode_builder/manifests/libnl

+[manifest]
+name = libnl
+
+[download]
+url = https://www.infradead.org/~tgr/libnl/files/libnl-3.2.25.tar.gz
+sha256 = 8beb7590674957b931de6b7f81c530b85dc7c1ad8fbda015398bc1e8d1ce8ec5
+
+[build.os=linux]
+builder = autoconf
+subdir = libnl-3.2.25