net: context: log on net_pkt alloc fail
net: context: log on net_pkt alloc fail

Log an error when allocating a network packet for transmission fails.
This is a problem which can be solved by increasing
`CONFIG_NET_PKT_TX_COUNT`, but is currently hard to diagnose.

Signed-off-by: Jordan Yates <d74a90e280bbad1cc3646781a4e234b467b60fe1@data61.csiro.au>

finikorg/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr