drivers: wifi: esp_at: s/ntohs/htons/ after parsing port number

'struct sockaddr_in' should contain port number in network byte order. This
means that htons() macro should be used, instead of ntohs().

This was working before since both htons() and ntohs() end up in calling
BSWAP_16().

Signed-off-by: Marcin Niestroj <m.niestroj@emb.dev>