sdkconfig: Add CONFIG_LWIP_IPV6_AUTOCONFIG for IPv6 SLAAC (#67)

To use IPv6 we need proper SLAAC support which is not possible without this option.
Compile tested on esp32, esp32s2, esp32s3, esp32c3
Functionality tested in esp32 BasicHttpClient with some minor patches, IPv6 start to work.

No significant sketch size increase (probably within rounding bounds):
Before:
Wrote 875328 bytes (558896 compressed) at 0x00010000 in 9.0 seconds (effective 779.4 kbit/s)...
After:
Wrote 875328 bytes (558942 compressed) at 0x00010000 in 9.0 seconds (effective 779.8 kbit/s)...

This patch part of the efforts mentioned in espressif/arduino-esp32#6242

Proper IPv6 support also was requested in:
espressif/arduino-esp32#6626
espressif/arduino-esp32#6590
espressif/arduino-esp32#6283
espressif/arduino-esp32#6703
espressif/arduino-esp32#5624
espressif/arduino-esp32#1261
And many others.

Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

configs/defconfig.common

@@ -68,3 +68,4 @@ CONFIG_SPI_FLASH_WRITE_CHUNK_SIZE=4096
 # CONFIG_SPI_SLAVE_ISR_IN_IRAM is not set
 CONFIG_SPIRAM_MALLOC_ALWAYSINTERNAL=4096
 CONFIG_SPIRAM_MALLOC_RESERVE_INTERNAL=0
+CONFIG_LWIP_IPV6_AUTOCONFIG=y