Put SSDP constants in progmem (#3142)
Put SSDP constants in progmem (#3142)

* Put constant strings in progmem

* strlen -> strlen_P

lrmoreno007/Arduino,lrmoreno007/Arduino,wemos/Arduino,Lan-Hekary/Arduino,Lan-Hekary/Arduino,esp8266/Arduino,hallard/Arduino,hallard/Arduino,Lan-Hekary/Arduino,jes/Arduino,Juppit/Arduino,me-no-dev/Arduino,me-no-dev/Arduino,Adam5Wu/Arduino,hallard/Arduino,wemos/Arduino,jes/Arduino,me-no-dev/Arduino,esp8266/Arduino,Lan-Hekary/Arduino,jes/Arduino,Juppit/Arduino,Adam5Wu/Arduino,wemos/Arduino,Juppit/Arduino,Juppit/Arduino,jes/Arduino,wemos/Arduino,me-no-dev/Arduino,wemos/Arduino,lrmoreno007/Arduino,esp8266/Arduino,esp8266/Arduino,Adam5Wu/Arduino,hallard/Arduino,Adam5Wu/Arduino,sticilface/Arduino,me-no-dev/Arduino,sticilface/Arduino,sticilface/Arduino,Adam5Wu/Arduino,lrmoreno007/Arduino,lrmoreno007/Arduino,sticilface/Arduino,hallard/Arduino,jes/Arduino,Juppit/Arduino,esp8266/Arduino,Lan-Hekary/Arduino,sticilface/Arduino