linux(4): Move use_real_names knob to the linux.c

MI linux.[c|h] are the module independent in terms of the Linux emulation
layer (ie, intended for both ISA - 32 & 64 bit), analogue of MD linux.h.
There must be a code here that cannot be placed into the corresponding by
common sense MI source and header files, i.e., code is machine independent,
but ISA dependent.
For the use_real_names knob, the code must be placed into the
linux_socket.[c|h], however linux_socket is ISA dependent.

Approved by: re (cperciva)
MFC after: 2 weeks

(cherry picked from commit 32fdc75fe7276083d446964055b0de0e29970b7c)
(cherry picked from commit 884ea80d4ebbd2d8ff03d56eddc1dc64d49be908)