drivers: wifi: esp: increase default RX net_pkt allocation timeout

So far there was 100ms timeout on allocation of RX net_pkt. This is too
little for cases when lots of data are incoming on pretty
fast (e.g. 1Mbps) UART interface and application layer does not consume
received network packets fast enough. Up to now in such cases all
incoming data was processed from UART and there was no data loss when
utilizing hardware flow control. However there was high chance that data
processed from UART could not be passed further to network stack,
because of the 100ms net_pkt allocation timeout. This happens for
example when low priority application does not have enough time to run.

Increase default RX net_pkt allocation timeout from 100ms to 5s, so
there is much more time to process network packets. Such timeout should
not harm, because only a dedicated RX thread will be suspended for that
time, resulting in suspending UART traffic if hardware flow control is
supported.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>