Revert "fib_rules: fix error in backport of e9919a24d302"

This reverts commit b2fc3516.

Revert "fib_rules: return 0 directly if an exactly same rule"
"exists when NLM_F_EXCL not supplied"

This reverts commit 1fff19a9.

Change-Id: If18c802f64a41a83721e2ecf06136ac1ae8fa6cb
Signed-off-by: Sharath Chandra Vurukala <sharathv@codeaurora.org>