eth: mlx5: fix macsec dependency

eth: mlx5: fix macsec dependency

Configurations with mlx5 built-in but macsec=m fail to link:

x86_64-linux-ld: drivers/infiniband/hw/mlx5/macsec.o: in function `mlx5r_add_gid_macsec_operations':
macsec.c:(.text+0x77d): undefined reference to `macsec_netdev_is_offloaded'
x86_64-linux-ld: drivers/infiniband/hw/mlx5/macsec.o: in function `mlx5r_del_gid_macsec_operations':
macsec.c:(.text+0xe81): undefined reference to `macsec_netdev_is_offloaded'

Fix the dependency so this configuration cannot happen.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20260622124229.2444502-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>