buildroot

libsrtp: security bump to version 1.5.4

Fixes CVE-2015-6360: Prevent potential DoS attack due to lack of bounds
checking on RTP header CSRC count and extension header length.

Also, add a hash file.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>