net/posix-stack: fix sockaddr forward reference
net/posix-stack: fix sockaddr forward reference

Fix compilation failure caused by undefined 'struct sockaddr' with kernel
version < 4.11
See: https://github.com/torvalds/linux/commit/2618be7dccf8739b89e1906b64bd8d551af351e6

Change-Id: Idba4b8cf1bc7e3da5aca224d4dee6a980b7cca95
Signed-off-by: Jun He <05c4aea3b428e9f4cbf962ab56f389db00194977@arm.com>
Message-Id: <20200918051204.21447-1-05c4aea3b428e9f4cbf962ab56f389db00194977@arm.com>

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