[catpowder] Enhancement: add buffer pooling and multiple ring entries to XDP backend

[kyleholohan]

This PR allows for multiple RX/TX ring entries in the catpowder XDP backend. It also hooks the user memory region (UmemReg) into buffer pools to prevent additional buffer copies and allow for more efficient buffer allocation.

This PR addresses both #1438 and #1437.

One potential downside of this approach: receive buffers are a limited resource, and if the client holds too many receive buffers for too long, the buffer pool may become exhausted. In this case, the system will start to drop packets. Possibly this behavior should be configurable (i.e., the receive buffers should be copied out of the receive pool unless a "zero copy" config is enabled).

[github-actions]

libos = catpowder
commit id = be698e1

collapsed_stack	num_calls	cycles_per_call	nanoseconds_per_call	total_duration	percent_total_duration	total_duration_exclusive	percent_total_duration_exclusive
bgc::inetstack::poll;inetstack::layer4::poll_once	21757259	626	251	12698854183	46	12691656874	84
bgc::inetstack::poll	10878629	1459	584	14981144829	54	2282290646	15
ioc::network::libos::push	16145	3286	1331	47213825	0	47213825	0
bgc::inetstack::poll;inetstack::layer4::poll_once;inetstack::layer4::receive_batch	5707	2894	1122	7319297	0	7315704	0
bgc::inetstack::tcp::established::background;tcp::established::background::retransmitter	11438	455	181	5470433	0	5470433	0
ioc::network::libos::pushto	671	6278	2591	3780327	0	3780327	0
ioc::network::libos::pop	9180	487	194	3352893	0	3352893	0
bgc::inetstack::tcp::established::background	11451	1909	751	12812274	0	3270787	0
bgc::inetstack::tcp::established::background;tcp::established::background::acknowledger	11451	734	289	3151298	0	3151298	0
ioc::network::libos::connect	42	42699	17364	1741675	0	1741675	0
bgc::inetstack::tcp::established::background;tcp::established::background::sender	11395	865	332	919756	0	919756	0
demikernel::sgaalloc	6503	152	61	879807	0	879807	0
demikernel::sgafree	8748	124	50	649175	0	649175	0
bgc::inetstack::tcp::passiveopen::background	42	17023	6742	451022	0	451022	0
ioc::network::libos::close	46	6708	2693	301483	0	301483	0
bgc::inetstack::poll;inetstack::layer4::poll_once;inetstack::layer4::receive_batch;udp::receive	192	341	138	70667	0	70667	0
ioc::network::libos::accept	39	2397	944	51544	0	51544	0
bgc::inetstack::arp::background	7	2195	875	13843	0	13843	0
bgc::inetstack::icmp::background	1	2386	952	2867	0	2867	0

[github-actions]

libos = catnap
commit id = be698e1

collapsed_stack	num_calls	cycles_per_call	nanoseconds_per_call	total_duration	percent_total_duration	total_duration_exclusive	percent_total_duration_exclusive
bgc::catnap::transport::epoll	13692169	2791	1162	6935386480	100	6935386480	100
ioc::network::libos::push	17600	466	194	7499080	0	7499080	0
ioc::network::libos::pop	15335	481	201	5574954	0	5574954	0
ioc::network::libos::connect	50	155188	63761	2754716	0	2754716	0
demikernel::sgaalloc	11292	123	52	1208894	0	1208894	0
demikernel::sgafree	11540	79	33	903230	0	903230	0
ioc::network::libos::pushto	1561	381	164	617151	0	617151	0
ioc::network::libos::accept	25	13191	5576	415904	0	415904	0
ioc::network::libos::close	18	22926	9566	324501	0	324501	0