nss: add version 3.15.1

nss: add version 3.15.1

Network Security Services (NSS) is a set of libraries designed to support
cross-platform development of security-enabled client and server applications.
Applications built with NSS can support SSL v2 and v3, TLS, PKCS 5, PKCS 7,
PKCS 11, PKCS 12, S/MIME, X.509 v3 certificates, and other security standards.

[YOCTO #4096]

(From OE-Core rev: 22c146fd3e829b89c07a2019005e180e93fece5d)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>