USB: gadget: ether needs to select CRC32

Fix build error, ether uses/needs to select CRC32 config symbol:

ether.c:(.text+0x271480): undefined reference to `crc32_le'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>