Merge branch 'misc-vlan-cleanups'

Gal Pressman says:

====================
Misc vlan cleanups

This patch series addresses compilation issues with objtool when VLAN
support is disabled (CONFIG_VLAN_8021Q=n) and makes related improvements
to the VLAN infrastructure.

When CONFIG_VLAN_8021Q=n, CONFIG_OBJTOOL=y, and CONFIG_OBJTOOL_WERROR=y,
the following compilation error occurs:

drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.o: error: objtool: parse_mirred.isra.0+0x370: mlx5e_tc_act_vlan_add_push_action() missing __noreturn in .c/.h or NORETURN() in noreturns.h

The error occurs because objtool cannot determine that unreachable BUG()
calls in VLAN code paths are actually dead code when VLAN support is
disabled.

First patch makes is_vlan_dev() a stub when VLAN is not configured,
allows compile-out of VLAN-dependent dead code paths and resolves the
objtool compilation error.

Second patch replaces BUG() calls with WARN_ON_ONCE(), as the usage of
BUG() should be avoided.

Third patch uses the "kernel" way of testing whether an option is
configured as builtin/module, instead of open-coding it.

v2: https://lore.kernel.org/20250610072611.1647593-1-gal@nvidia.com/
====================

Link: https://patch.msgid.link/20250616132626.1749331-1-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>