net: nbuf: Add helper function to copy buf user_data
net: nbuf: Add helper function to copy buf user_data

The function copies the net_buf user data (struct net_nbuf).

Change-Id: I2ea42823d58aea77ea7b710f6ce5fd5d1e3641b4
Signed-off-by: Jukka Rissanen <f9f077d1da4c7aa947f9864fa5a28c3588f6a45d@linux.intel.com>

fbsder/zephyr,fbsder/zephyr,fbsder/zephyr,fbsder/zephyr,fbsder/zephyr