Switch to native NAPI polling, as this reduces overhead and complexity.

Normal path is faster, since one cmpxchg() is not anymore requested,
and busy polling with the NAPI polling has same performance.

Tested:
lpk50:~# cat /proc/sys/net/core/busy_read
70
lpk50:~# nstat >/dev/null;./netperf -H lpk55 -t TCP_RR;nstat
MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to lpk55.prod.google.com () port 0 AF_INET : first burst 0
Local /Remote
Socket Size   Request  Resp.   Elapsed  Trans.
Send   Recv   Size     Size    Time     Rate
bytes  Bytes  bytes    bytes   secs.    per sec

16384  87380  1        1       10.00    40095.07
16384  87380
IpInReceives                    401062             0.0
IpInDelivers                    401062             0.0
IpOutRequests                   401079             0.0
TcpActiveOpens                  7                  0.0
TcpPassiveOpens                 3                  0.0
TcpAttemptFails                 3                  0.0
TcpEstabResets                  5                  0.0
TcpInSegs                       401036             0.0
TcpOutSegs                      401052             0.0
TcpOutRsts                      38                 0.0
UdpInDatagrams                  26                 0.0
UdpOutDatagrams                 27                 0.0
Ip6OutNoRoutes                  1                  0.0
TcpExtDelayedACKs               1                  0.0
TcpExtTCPPrequeued              98                 0.0
TcpExtTCPDirectCopyFromPrequeue 98                 0.0
TcpExtTCPHPHits                 4                  0.0
TcpExtTCPHPHitsToUser           98                 0.0
TcpExtTCPPureAcks               5                  0.0
TcpExtTCPHPAcks                 101                0.0
TcpExtTCPAbortOnData            6                  0.0
TcpExtBusyPollRxPackets         400832             0.0
TcpExtTCPOrigDataSent           400983             0.0
IpExtInOctets                   21273867           0.0
IpExtOutOctets                  21261254           0.0
IpExtInNoECTPkts                401064             0.0
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>