[syslog] Use C++17 nested namespace syntax (#12594)

esphome/components/syslog/esphome_syslog.cpp

@@ -4,8 +4,7 @@
 #include "esphome/core/application.h"
 #include "esphome/core/time.h"
 
-namespace esphome {
-namespace syslog {
+namespace esphome::syslog {
 
 // Map log levels to syslog severity using an array, indexed by ESPHome log level (1-7)
 constexpr int LOG_LEVEL_TO_SYSLOG_SEVERITY[] = {
@@ -54,5 +53,4 @@ void Syslog::log_(const int level, const char *tag, const char *message, size_t
   this->parent_->send_packet((const uint8_t *) data.data(), data.size());
 }
 
-}  // namespace syslog
-}  // namespace esphome
+}  // namespace esphome::syslog

esphome/components/syslog/esphome_syslog.h

@@ -7,8 +7,7 @@
 #include "esphome/components/time/real_time_clock.h"
 
 #ifdef USE_NETWORK
-namespace esphome {
-namespace syslog {
+namespace esphome::syslog {
 class Syslog : public Component, public Parented<udp::UDPComponent>, public logger::LogListener {
  public:
   Syslog(int level, time::RealTimeClock *time) : log_level_(level), time_(time) {}
@@ -24,6 +23,5 @@ class Syslog : public Component, public Parented<udp::UDPComponent>, public logg
   bool strip_{true};
   int facility_{16};
 };
-}  // namespace syslog
-}  // namespace esphome
+}  // namespace esphome::syslog
 #endif