MFC: ENA netmap support and bug fixes

r363638 Fix ENA build when integrated into kernel
r354242 Make valdiate_rx_req_id static inline because it uses other static
r354225 Update ENA version to v2.1.0
r354224 Add support for ENA NETMAP partial initialization
r354223 Add support for ENA NETMAP Tx
r354222 Add support for ENA NETMAP Rx
r354221 Introduce NETMAP support in ENA
r354220 Split Rx/Tx from initialization code in ENA driver
r354219 Fix ENA keep-alive timeout due to prolonged reset
r354218 Add WC support for arm64 in the ENA driver

Obtained from: Semihalf
Sponsored by: Amazon, Inc.