Do not read-lock NIC recursively

A deadlock may occur if a write lock on a RWMutex is blocked between
nested read lock attempts as the inner read lock attempt will be
blocked in this scenario.

Example (T1 and T2 are differnt goroutines):
  T1: obtain read-lock
  T2: attempt write-lock (blocks)
  T1: attempt inner/nested read-lock (blocks)

Here we can see that T1 and T2 are deadlocked.

Tests: Existing tests pass.
PiperOrigin-RevId: 298426678

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