cxgbe(4): netmap support for Terminator 5 (T5) based 10G/40G cards.
Netmap gets its own hardware-assisted virtual interface and won't take
over or disrupt the "normal" interface in any way.  You can use both
simultaneously.

For kernels with DEV_NETMAP, cxgbe(4) carves out an ncxl<N> interface
(note the 'n' prefix) in the hardware to accompany each cxl<N>
interface.  These two ifnet's per port share the same wire but really
are separate interfaces in the hardware and software.  Each gets its own
L2 MAC addresses (unicast and multicast), MTU, checksum caps, etc.  You
should run netmap on the 'n' interfaces only, that's what they are for.

With this, pkt-gen is able to transmit > 45Mpps out of a single 40G port
of a T580 card.  2 port tx is at ~56Mpps total (28M + 28M) as of now.
Single port receive is at 33Mpps but this is very much a work in
progress.  I expect it to be closer to 40Mpps once done.  In any case
the current effort can already saturate multiple 10G ports of a T5 card
at the smallest legal packet size.  T4 gear is totally untested.

trantor:~# ./pkt-gen -i ncxl0 -f tx -D 00:07:43:ab:cd:ef
881.952141 main [1621] interface is ncxl0
881.952250 extract_ip_range [275] range is 10.0.0.1:0 to 10.0.0.1:0
881.952253 extract_ip_range [275] range is 10.1.0.1:0 to 10.1.0.1:0
881.962540 main [1804] mapped 334980KB at 0x801dff000
Sending on netmap:ncxl0: 4 queues, 1 threads and 1 cpus.
10.0.0.1 -> 10.1.0.1 (00:00:00:00:00:00 -> 00:07:43:ab:cd:ef)
881.962562 main [1882] Sending 512 packets every  0.000000000 s
881.962563 main [1884] Wait 2 secs for phy reset
884.088516 main [1886] Ready...
884.088535 nm_open [457] overriding ifname ncxl0 ringid 0x0 flags 0x1
884.088607 sender_body [996] start
884.093246 sender_body [1064] drop copy
885.090435 main_thread [1418] 45206353 pps (45289533 pkts in 1001840 usec)
886.091600 main_thread [1418] 45322792 pps (45375593 pkts in 1001165 usec)
887.092435 main_thread [1418] 45313992 pps (45351784 pkts in 1000834 usec)
888.094434 main_thread [1418] 45315765 pps (45406397 pkts in 1002000 usec)
889.095434 main_thread [1418] 45333218 pps (45378551 pkts in 1001000 usec)
890.097434 main_thread [1418] 45315247 pps (45405877 pkts in 1002000 usec)
891.099434 main_thread [1418] 45326515 pps (45417168 pkts in 1002000 usec)
892.101434 main_thread [1418] 45333039 pps (45423705 pkts in 1002000 usec)
893.103434 main_thread [1418] 45324105 pps (45414708 pkts in 1001999 usec)
894.105434 main_thread [1418] 45318042 pps (45408723 pkts in 1002001 usec)
895.106434 main_thread [1418] 45332430 pps (45377762 pkts in 1001000 usec)
896.107434 main_thread [1418] 45338072 pps (45383410 pkts in 1001000 usec)
...

Relnotes:	Yes
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