rpc: fix LZ4_DECODER_RING_BUFFER_SIZE not defined
rpc: fix LZ4_DECODER_RING_BUFFER_SIZE not defined

LZ4_DECODER_RING_BUFFER_SIZE macro is introduced in lz4 since v1.8.2.
On popular distros like ubuntu-18.04/centos-8 who don't provide recent
lz4 lib the building will fail.

This patch fixes "not declared" failure by copying the same definition in lz4 here

Change-Id: I4cc87c7caca4ee4858df10609fdca059707e4ba1
Signed-off-by: Jun He <05c4aea3b428e9f4cbf962ab56f389db00194977@arm.com>
Message-Id: <20200918025401.27397-1-05c4aea3b428e9f4cbf962ab56f389db00194977@arm.com>

dreamsxin/seastar,avikivity/seastar,cloudius-systems/seastar,avikivity/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,scylladb/seastar,avikivity/seastar,syuu1228/seastar,scylladb/seastar,dreamsxin/seastar,dreamsxin/seastar,cloudius-systems/seastar