Consistent spelling of GA/PA

[spacegaier]

esp-knx-ip/esp-knx-ip.h

Line 475 in eff9365

static address_t GA_to_address(uint8_t area, uint8_t line, uint8_t member)

esp-knx-ip/esp-knx-ip.h

Line 482 in eff9365

static address_t PA_to_address(uint8_t area, uint8_t line, uint8_t member)

GA_to_address() and PA_to_address() are the only methods where GA and PA are spelled with capital letters. Everywhere else they are lower letters. This is a bit inconsistent and confusing.