macsec: use NLA_UINT for MACSEC_SA_ATTR_PN

macsec: use NLA_UINT for MACSEC_SA_ATTR_PN

MACSEC_SA_ATTR_PN is either a u32 or a u64, we can now use NLA_UINT
for this instead of a custom binary type. We can then use a min check
within the policy.

We need to keep the length checks done in macsec_{add,upd}_{rx,tx}sa
based on whether the device is set up for XPN (with 64b PNs instead of
32b).

On the dump side, keep the existing custom code as userspace may
expect a u64 when using XPN, and nla_put_uint may only output a u32
attribute if the value fits.

Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/c9d32bd479cd4464e09010fbce1becc75377c8a0.1756202772.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>