net: netmem: remove NET_IOV_MAX from net_iov_type enum

Remove the NET_IOV_MAX workaround from the net_iov_type enum. This entry
was previously added to force the enum size to unsigned long to satisfy
the NET_IOV_ASSERT_OFFSET static assertions.

After commit f3d85c9ee510 ("netmem: introduce struct netmem_desc
mirroring struct page") this approach became unnecessary by placing the
net_iov_type after the netmem_desc. Placing the net_iov_type after
netmem_desc results in the net_iov_type size having no effect on the
position or layout of the fields that mirror the struct page.

The layout before this patch:

struct net_iov {
union {
struct netmem_desc desc; /* 0 48 */
struct {
long unsigned int _flags; /* 0 8 */
long unsigned int pp_magic; /* 8 8 */
struct page_pool * pp; /* 16 8 */
long unsigned int _pp_mapping_pad; /* 24 8 */
long unsigned int dma_addr; /* 32 8 */
atomic_long_t pp_ref_count; /* 40 8 */
}; /* 0 48 */
}; /* 0 48 */
struct net_iov_area * owner; /* 48 8 */
enum net_iov_type type; /* 56 8 */

/* size: 64, cachelines: 1, members: 3 */
};

The layout after this patch:

struct net_iov {
union {
struct netmem_desc desc; /* 0 48 */
struct {
long unsigned int _flags; /* 0 8 */
long unsigned int pp_magic; /* 8 8 */
struct page_pool * pp; /* 16 8 */
long unsigned int _pp_mapping_pad; /* 24 8 */
long unsigned int dma_addr; /* 32 8 */
atomic_long_t pp_ref_count; /* 40 8 */
}; /* 0 48 */
}; /* 0 48 */
struct net_iov_area * owner; /* 48 8 */
enum net_iov_type type; /* 56 4 */

/* size: 64, cachelines: 1, members: 3 */
/* padding: 4 */
};

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20251024-b4-devmem-remove-niov-max-v1-1-ba72c68bc869@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>