Bluetooth: SMP: Fix NULL backend compilation
Bluetooth: SMP: Fix NULL backend compilation

This was not building due to bt_l2cap_create_pdu API change.

  CC      net/bluetooth/smp_null.o
net/bluetooth/smp_null.c: In function 'bt_smp_recv':
net/bluetooth/smp_null.c:59:2: warning: passing argument 1 of 'bt_l2cap_create_pdu' from incompatible pointer type [enabled by default]
  buf = bt_l2cap_create_pdu(conn);
  ^
In file included from net/bluetooth/smp_null.c:32:0:
net/bluetooth/l2cap_internal.h:136:17: note: expected 'struct nano_fifo *' but argument is of type 'struct bt_conn *'
 struct net_buf *bt_l2cap_create_pdu(struct nano_fifo *fifo);

Change-Id: I5fd8ce63da09af1c123b1092624d48edc009756b
Signed-off-by: Szymon Janc <b8f563e108973ccd513fe259bc96c595c4d39939@tieto.com>

galak/zephyr,coldnew/zephyr-project-fork,pklazy/zephyr,fractalclone/zephyr-riscv,Vudentz/zephyr,jamesonwilliams/zephyr-kernel,kraj/zephyr,zephyriot/zephyr,runchip/zephyr-cc3200,zephyrproject-rtos/zephyr,sharronliu/zephyr,fbsder/zephyr,finikorg/zephyr,zephyriot/zephyr,erwango/zephyr,Vudentz/zephyr,fractalclone/zephyr-riscv,32bitmicro/zephyr,galak/zephyr,jamesonwilliams/zephyr-kernel,holtmann/zephyr,sharronliu/zephyr,mirzak/zephyr-os,Vudentz/zephyr,zephyriot/zephyr,fbsder/zephyr,jamesonwilliams/zephyr-kernel,aceofall/zephyr-iotos,punitvara/zephyr,erwango/zephyr,fractalclone/zephyr-riscv,Vudentz/zephyr,runchip/zephyr-cc3200,runchip/zephyr-cc3200,runchip/zephyr-cc3220,pklazy/zephyr,finikorg/zephyr,sharronliu/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,holtmann/zephyr,fbsder/zephyr,mbolivar/zephyr,bboozzoo/zephyr,bigdinotech/zephyr,32bitmicro/zephyr,aceofall/zephyr-iotos,erwango/zephyr,explora26/zephyr,bboozzoo/zephyr,bigdinotech/zephyr,punitvara/zephyr,jamesonwilliams/zephyr-kernel,Vudentz/zephyr,jamesonwilliams/zephyr-kernel,tidyjiang8/zephyr-doc,fractalclone/zephyr-riscv,zephyrproject-rtos/zephyr,ldts/zephyr,mirzak/zephyr-os,runchip/zephyr-cc3220,nashif/zephyr,finikorg/zephyr,galak/zephyr,zephyriot/zephyr,mirzak/zephyr-os,nashif/zephyr,kraj/zephyr,kraj/zephyr,pklazy/zephyr,holtmann/zephyr,GiulianoFranchetto/zephyr,mbolivar/zephyr,tidyjiang8/zephyr-doc,explora26/zephyr,coldnew/zephyr-project-fork,mbolivar/zephyr,punitvara/zephyr,bboozzoo/zephyr,rsalveti/zephyr,bboozzoo/zephyr,nashif/zephyr,ldts/zephyr,erwango/zephyr,bigdinotech/zephyr,mirzak/zephyr-os,mirzak/zephyr-os,runchip/zephyr-cc3220,fbsder/zephyr,ldts/zephyr,fbsder/zephyr,runchip/zephyr-cc3220,holtmann/zephyr,rsalveti/zephyr,sharronliu/zephyr,coldnew/zephyr-project-fork,aceofall/zephyr-iotos,GiulianoFranchetto/zephyr,tidyjiang8/zephyr-doc,mbolivar/zephyr,32bitmicro/zephyr,ldts/zephyr,explora26/zephyr,GiulianoFranchetto/zephyr,holtmann/zephyr,zephyrproject-rtos/zephyr,coldnew/zephyr-project-fork,zephyrproject-rtos/zephyr,ldts/zephyr,fractalclone/zephyr-riscv,aceofall/zephyr-iotos,finikorg/zephyr,rsalveti/zephyr,GiulianoFranchetto/zephyr,runchip/zephyr-cc3200,galak/zephyr,galak/zephyr,explora26/zephyr,pklazy/zephyr,32bitmicro/zephyr,kraj/zephyr,bboozzoo/zephyr,rsalveti/zephyr,kraj/zephyr,Vudentz/zephyr,zephyriot/zephyr,rsalveti/zephyr,coldnew/zephyr-project-fork,bigdinotech/zephyr,punitvara/zephyr,erwango/zephyr,zephyrproject-rtos/zephyr,aceofall/zephyr-iotos,bigdinotech/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,tidyjiang8/zephyr-doc,pklazy/zephyr,tidyjiang8/zephyr-doc,mbolivar/zephyr,runchip/zephyr-cc3200,32bitmicro/zephyr,sharronliu/zephyr,nashif/zephyr,explora26/zephyr