BACKPORT: UPSTREAM: Add a eBPF helper function to retrieve socket uid

Cherry-pick from commit 6acc5c2910689fc6ee181bf63085c5efff6a42bd

Returns the owner uid of the socket inside a sk_buff. This is useful to
perform per-UID accounting of network traffic or per-UID packet
filtering. The socket need to be a fullsock otherwise overflowuid is
returned.

Signed-off-by: Chenbo Feng <fengc@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Bug: 30950746
Change-Id: Idc00947ccfdd4e9f2214ffc4178d701cd9ead0ac
Signed-off-by: Chatur27 <jasonbright2709@gmail.com>