ath6kl: remove redundant variables netlen, orig_buf, orig_len, dropped and stats

Variables netlen, orig_buf, orig_len, dropped and stats are assigned values
but are never used hence they are redundant and can be removed.

Cleans up clang warnings:
warning: variable 'netlen' set but not used [-Wunused-but-set-variable]
warning: variable 'orig_buf' set but not used [-Wunused-but-set-variable]
warning: variable 'orig_len' set but not used [-Wunused-but-set-variable]
warning: variable 'dropped' set but not used [-Wunused-but-set-variable]
warning: variable 'stats' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>