net: ipa: three small fixes

Some time ago changes were made to stop referring to clearing the
hardware pipeline as a "tag process."  Fix a comment to use the
newer terminology.

Get rid of a pointless double-negation of the Boolean toward_ipa
flag in ipa_endpoint_config().

make ipa_endpoint_exit_one() private; it's only referenced inside
"ipa_endpoint.c".

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>