gnrc_netif/lorawan: drop netif header on send

[jia200x]

Contribution description

This PR fixes a memory leak introduced by #16080. The netif hdr was not being released on send.

Testing procedure

On current master:

ifconfig 3 up
2021-06-24 15:24:51,325 # ifconfig 3 up
> ifconfig
2021-06-24 15:25:06,809 # ifconfig
2021-06-24 15:25:06,820 # Iface  3  HWaddr: 26:01:44:AF  Frequency: 869524963Hz  RSSI: 99  BW: 125kHz  SF: 12  CR: 4/5  Link: up 
2021-06-24 15:25:06,827 #            TX-Power: 14dBm  State: SLEEP  Demod margin.: 0  Num gateways.: 0 
2021-06-24 15:25:06,829 #           IQ_INVERT  
2021-06-24 15:25:06,833 #           RX_SINGLE  OTAA  L2-PDU:767  
2021-06-24 15:25:06,834 #           
txtsnd 3 01 "THIS IS RIOT!"
2021-06-24 15:26:25,320 # txtsnd 3 01 "THIS IS RIOT!"
> txtsnd 3 01 "THIS IS RIOT!"
2021-06-24 15:26:29,540 # txtsnd 3 01 "THIS IS RIOT!"
> pktbuf
2021-06-24 15:26:32,857 # pktbuf
2021-06-24 15:26:32,864 # packet buffer: first byte: 0x2000119c, last byte: 0x2000139c (size: 512)
2021-06-24 15:26:32,866 #   position of last byte used: 120
2021-06-24 15:26:32,872 # =========== chunk   0 (0x2000119c size:  120) ===========
2021-06-24 15:26:32,879 # 00000000  00  00  00  00  B4  11  00  20  0D  00  00  00  01  00  00  00
2021-06-24 15:26:32,885 # 00000010  00  00  00  00  00  00  00  00  70  7C  9F  54  84  06  8F  42
2021-06-24 15:26:32,892 # 00000020  BD  69  C1  24  3B  18  4F  84  9C  11  00  20  DC  11  00  20
2021-06-24 15:26:32,899 # 00000030  09  00  00  00  01  00  00  00  FF  00  00  00  00  00  00  00
2021-06-24 15:26:32,905 # 00000040  00  01  00  00  00  00  00  80  01  00  00  00  00  00  00  00
2021-06-24 15:26:32,912 # 00000050  9C  11  00  20  04  12  00  20  09  00  00  00  01  00  00  00
2021-06-24 15:26:32,919 # 00000060  FF  00  00  00  00  00  00  00  00  01  00  00  00  00  00  80
2021-06-24 15:26:32,922 # 00000070  01  00  00  00  00  00  00  00
2021-06-24 15:26:32,927 # ~ unused: 0x20001214 (next: (nil), size:  392) ~

With this PR:

2021-06-24 15:22:42,977 # ifconfig 3 up
> ifconfig
2021-06-24 15:22:53,247 # ifconfig
2021-06-24 15:22:53,258 # Iface  3  HWaddr: 26:01:4F:A0  Frequency: 869524963Hz  RSSI: 99  BW: 125kHz  SF: 12  CR: 4/5  Link: up 
2021-06-24 15:22:53,265 #            TX-Power: 14dBm  State: SLEEP  Demod margin.: 0  Num gateways.: 0 
2021-06-24 15:22:53,267 #           IQ_INVERT  
2021-06-24 15:22:53,271 #           RX_SINGLE  OTAA  L2-PDU:767  
2021-06-24 15:22:53,272 #           
txtsnd 3 01 "THIS IS RIOT!"
2021-06-24 15:22:58,717 # txtsnd 3 01 "THIS IS RIOT!"
ifconfig 3 set dr 5
2021-06-24 15:23:14,571 # ifconfig 3 set dr 5
2021-06-24 15:23:14,576 # success: set datarate on interface 3 to 5
txtsnd 3 01 "THIS IS RIOT!"
2021-06-24 15:23:16,002 # txtsnd 3 01 "THIS IS RIOT!"
> txtsnd 3 01 "THIS IS RIOT!"
2021-06-24 15:23:23,133 # txtsnd 3 01 "THIS IS RIOT!"
> txtsnd 3 01 "THIS IS RIOT!"
2021-06-24 15:23:36,768 # txtsnd 3 01 "THIS IS RIOT!"
> 2021-06-24 15:23:37,889 # PKTDUMP: data received:
2021-06-24 15:23:37,894 # ~~ SNIP  0 - size:   4 byte, type: NETTYPE_UNDEF (0)
2021-06-24 15:23:37,897 # 00000000  DE  AD  BE  EF
2021-06-24 15:23:37,901 # ~~ SNIP  1 - size:   9 byte, type: NETTYPE_NETIF (-1)
2021-06-24 15:23:37,905 # if_pid: 3  rssi: -32768  lqi: 0
2021-06-24 15:23:37,905 # flags: 0x0
2021-06-24 15:23:37,907 # src_l2addr: (nil)
2021-06-24 15:23:37,908 # dst_l2addr: 01
2021-06-24 15:23:37,912 # ~~ PKT    -  2 snips, total size:  13 byte
pktbuf
2021-06-24 15:23:44,918 # pktbuf
2021-06-24 15:23:44,924 # packet buffer: first byte: 0x2000119c, last byte: 0x2000139c (size: 512)
2021-06-24 15:23:44,928 #   position of last byte used: 128
2021-06-24 15:23:44,933 # ~ unused: 0x2000119c (next: (nil), size:  512) ~

Issues/PRs references

#16080

[MrKevinWeiss]

It seems sound, test output is provided, and a test will be added to the release test.

ACK!