Code under GSM_SLEEP causes compilation errors for Discovery board

[garyachy]

drivers/network/gsm_ll.c:185:3: warning: implicit declaration of function 'strnlen' [-Wimplicit-function-declaration]
len = strnlen(buf, MAX_BUF_LEN) + 1;
^
In file included from OS/Chibios/os/hal/include/pal.h:113:0,
from OS/Chibios/os/hal/include/hal.h:45,
from common/include/common.h:27,
from drivers/network/gsm_ll.c:30:
drivers/network/gsm_ll.c: In function 'gsmTask':
drivers/network/gsm_ll.c:712:28: error: 'GPIOA_PIN6' undeclared (first use in this function)
palClearPad(GPIOA, GPIOA_PIN6);
^
OS/Chibios/os/hal/ports/STM32/LLD/GPIOv2/pal_lld.h:428:74: note: in definition of macro 'pal_lld_clearport'
#define pal_lld_clearport(port, bits) ((port)->BSRR.H.clear = (uint16_t)(bits))
^
OS/Chibios/os/hal/include/pal.h:482:32: note: in expansion of macro 'palClearPort'
#define palClearPad(port, pad) palClearPort(port, PAL_PORT_BIT(pad))
^
OS/Chibios/os/hal/include/pal.h:482:51: note: in expansion of macro 'PAL_PORT_BIT'
#define palClearPad(port, pad) palClearPort(port, PAL_PORT_BIT(pad))
^
drivers/network/gsm_ll.c:712:9: note: in expansion of macro 'palClearPad'
palClearPad(GPIOA, GPIOA_PIN6);
^
drivers/network/gsm_ll.c:712:28: note: each undeclared identifier is reported only once for each function it appears in
palClearPad(GPIOA, GPIOA_PIN6);
^
OS/Chibios/os/hal/ports/STM32/LLD/GPIOv2/pal_lld.h:428:74: note: in definition of macro 'pal_lld_clearport'
#define pal_lld_clearport(port, bits) ((port)->BSRR.H.clear = (uint16_t)(bits))
^
OS/Chibios/os/hal/include/pal.h:482:32: note: in expansion of macro 'palClearPort'
#define palClearPad(port, pad) palClearPort(port, PAL_PORT_BIT(pad))
^
OS/Chibios/os/hal/include/pal.h:482:51: note: in expansion of macro 'PAL_PORT_BIT'
#define palClearPad(port, pad) palClearPort(port, PAL_PORT_BIT(pad))
^
drivers/network/gsm_ll.c:712:9: note: in expansion of macro 'palClearPad'
palClearPad(GPIOA, GPIOA_PIN6);
^