netconsole: introduce helpers for dynamic_netconsole_mutex lock/unlock

netconsole: introduce helpers for dynamic_netconsole_mutex lock/unlock

This commit introduces two helper functions to perform lock/unlock on
dynamic_netconsole_mutex providing no-op stub versions when compiled
without CONFIG_NETCONSOLE_DYNAMIC and refactors existing call sites to
use the new helpers.

This is done following kernel coding style guidelines, in preparation
for an upcoming change. It avoids the need for preprocessor conditionals
in the call site and keeps the logic easier to follow.

Signed-off-by: Andre Carvalho <asantostc@gmail.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Tested-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260118-netcons-retrigger-v11-5-4de36aebcf48@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>