RDMA/rxe: Add net namespace support for IPv4/IPv6 sockets

RDMA/rxe: Add net namespace support for IPv4/IPv6 sockets

Add a net namespace implementation file to rxe to manage the
lifecycle of IPv4 and IPv6 sockets per network namespace.

This implementation handles the creation and destruction of the
sockets both for init_net and for dynamically created network
namespaces. The sockets are initialized when a namespace becomes
active and are properly released when the namespace is removed.

This change provides the infrastructure needed for rxe to operate
correctly in environments using multiple network namespaces.

Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Link: https://patch.msgid.link/20260313023058.13020-3-yanjun.zhu@linux.dev
Signed-off-by: Leon Romanovsky <leon@kernel.org>