Fix slow SNTP sync from cold boot

[petermm]

using ap_sta_network example https://github.com/atomvm/AtomVM/blob/release-0.6/examples/erlang/esp32/ap_sta_network.erl

testing on real devices (and hundreds of wokwi ci runs) - a cold boot often produces a significant wait for sntp sync: 20-30 seconds.

calling esp_sntp_restart() on the got_ip event fixes this. the function is noop if sntp is not init'ed/config'ed. https://github.com/espressif/esp-idf/blob/707d097b01756687cca18be855a2675d150247ae/components/lwip/apps/sntp/sntp.c#L123

These changes are made under both the "Apache 2.0" and the "GNU Lesser General Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later