Value initialize pthread_t class members in constructor

[pudelkoM]

We should make sure all pthread_t class members are initialized, but pthread_t is a opaque value which can map to a struct, pointer, or numeric type. Therefore, the safest approach is value initialization and letting the compiler do the right thing.

POSIX.1 allows an implementation wide freedom in choosing the type used to represent a thread ID; for example,
representation using either an arithmetic type or a structure is permitted.

Example playground: https://cpp.godbolt.org/z/f63cf48hn

[codecov]

Codecov Report

Merging #812 (341778e) into main (9d9770f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #812   +/-   ##
=======================================
  Coverage   78.61%   78.61%           
=======================================
  Files         334      334           
  Lines       30003    30006    +3     
=======================================
+ Hits        23587    23590    +3     
  Misses       6416     6416           

Impacted Files	Coverage Δ
stratum/hal/lib/barefoot/bfrt_packetio_manager.cc	87.10% <100.00%> (ø)
stratum/hal/lib/bcm/bcm_packetio_manager.h	100.00% <100.00%> (ø)
stratum/hal/lib/common/hal.cc	78.18% <100.00%> (ø)
stratum/hal/lib/phal/attribute_database.h	100.00% <100.00%> (ø)
stratum/hal/lib/phal/onlp/onlp_event_handler.h	100.00% <100.00%> (ø)
stratum/hal/lib/phal/udev_event_handler.h	100.00% <100.00%> (ø)
stratum/lib/security/auth_policy_checker.cc	31.03% <100.00%> (ø)
stratum/procmon/procmon.cc	84.15% <100.00%> (ø)
stratum/hal/lib/phal/attribute_database.cc	59.47% <0.00%> (ø)