services: ntp: Fix a crash when using legacy configuration.
Fixes issue #37504 (see: https://bugs.gnu.org/37504).
The bug was caused by the fact that destructuring an <ntp-configuration>
record using match would bind the 'servers' field without using the
compatibility accessor.
* gnu/services/networking.scm (ntp-shepherd-service): Replace `match-lambda'
by distinct `lambda' and `match' calls, so that the 'servers' field can be
generated by applying the `ntp-configuration-servers' procedure to the
configuration object.