samples: net: wifi: boards: rdrw612bga: Modify CONFIG_POSIX_MAX_FDS config.

[Reproduce issue]
1. Connect In-STA to Ex-AP
   wifi connect WiFi_STA_HE_1.1.8 1234567890 3 2 2

2. Start APUT with ACS using below commands
   wifi ap enable nxp-AP 161 1234567890 3

3. Connect Ex-STA to APUT and verify association using ping traffic

4. Now start two TCP server
  zperf tcp download -I ml 5001 192.168.0.252
  zperf tcp download -I up 6002 192.168.10.1

Observed behavior:
=============

Second TCP server fails to start

[Analysis]
1. After starting uap and a tcp server,
   there is only one allocatable fd resource
   left in the fdtable.
2. When two TCP clients try to establish a connection
   with the server at the same time, the second client
   cannot be assigned an fd, resulting in a failure.

[Fix]
Increase the maximum number of open file descriptors.

Signed-off-by: Qiankun Li <[email protected]>

Author: Liam-qk

samples/net/wifi/boards/rd_rw612_bga.conf

@@ -22,7 +22,7 @@ CONFIG_EVENTS=y
 CONFIG_SYS_HEAP_AUTO=y
 CONFIG_HEAP_MEM_POOL_SIZE=122880
 CONFIG_SCHED_MULTIQ=y
-CONFIG_POSIX_MAX_FDS=20
+CONFIG_POSIX_MAX_FDS=30
 CONFIG_ZVFS_OPEN_MAX=20
 
 # shell