feat: add configurable syslog severity level filter

[PhilipLykov]

Summary

• Add configurable syslog severity level filter to reduce syslog noise
• Add LogLevel enum and rsyslog_level field (tag 12) to NetworkConfig protobuf
• Wire the new config field to the existing Syslog::logMask() filtering mechanism via a new syslogLevelToMask() helper
• Default behavior: UNSET (0) is treated as INFO, filtering out DEBUG messages

Motivation

Currently the firmware forwards all log messages to the configured rsyslog server with no way to filter by severity. This generates significant traffic from DEBUG messages that are rarely needed in production. The Syslog class already has a _priMask filtering mechanism, but it was never wired to a user-configurable setting.

Changes

File	Change
src/mesh/generated/meshtastic/config.pb.h	Add LogLevel enum, rsyslog_level field, tags, FIELDLIST, init macros, size updates
src/DebugConfiguration.h	Add syslogLevelToMask() inline helper function
src/mesh/eth/ethClient.cpp	Apply logMask() during Ethernet syslog initialization
src/mesh/wifi/WiFiAPClient.cpp	Apply logMask() during WiFi syslog initialization

Companion PR

Protobuf definition: meshtastic/protobufs#870

Backwards Compatibility

• Default (UNSET = 0) maps to INFO level - existing devices will filter out DEBUG after upgrade
• No breaking changes to wire format or existing config fields
• Apps that don't set rsyslog_level get sensible default behavior

Test plan

• Firmware builds successfully for rak4631_eth_gw
• Verify DEBUG messages are filtered by default on rsyslog server
• Set rsyslog_level to LOG_DEBUG and verify all messages appear
• Set rsyslog_level to LOG_WARNING and verify only WARNING/ERROR/CRITICAL appear
• Verify WiFi-based syslog filtering works on ESP32

[caveman99]

Please revert the change to the 'generated' file. This will casue ugly merge conflicts when the protos re re-generated

[PhilipLykov]

@caveman99 Thanks for the review! Both points addressed in ca5a0e2:

1. Generated file reverted — config.pb.h is now back to the upstream version. The proto definition lives in the companion PR meshtastic/protobufs#870. The rsyslog_level usage in firmware is now guarded with #ifdef meshtastic_Config_NetworkConfig_rsyslog_level_tag, so the code compiles cleanly with or without the proto field — defaulting to INFO when absent.

2. TRACE level — Made it an explicit case with a comment explaining that syslog has no native TRACE level, so it maps to SYSLOG_DEBUG (the most verbose syslog level available):

case 5: // LOG_TRACE — syslog has no TRACE; map to DEBUG (most verbose syslog level)
    return LOG_UPTO(SYSLOG_DEBUG);
case 10: // LOG_DEBUG
    return LOG_UPTO(SYSLOG_DEBUG);

Also merged latest upstream/develop — no conflicts.

[llamafilm]

The name of the protocol is 'syslog', not 'rsyslog'. It's defined by RFC 3164 and RFC 5424. Rsyslog is just one software implementation of said protocol.

[PhilipLykov]

@llamafilm Good point — "syslog" is indeed the protocol name (RFC 3164/5424), and "rsyslog" is just one implementation. However, the existing config field is already named rsyslog_server in the Meshtastic protobuf, so we named rsyslog_level to be consistent with that established convention. Renaming would be a separate discussion affecting the existing field as well.