bpf, sockmap: Fix map type error in sock_map_del_link

sock_map_del_link() operates on both SOCKMAP and SOCKHASH, although
both types have member named "progs", the offset of "progs" member in
these two types is different, so "progs" should be accessed with the
real map type.

Fixes: 604326b4

 ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/r/20230804073740.194770-2-xukuohai@huaweicloud.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>