StdLib/BsdSocketLib: Fix function declaration mismatch with definition.

Replace the existing old-style function declarations for Field, cvtbase and spectHex in BsdSocketLib with real prototypes.  This allows StdLib to build using the GCC48 toolchain.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Bruce Cran <bruce.cran@gmail.com>
Reviewed-by: Daryl McDaniel <daryl.mcdaniel@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16467 6f19259b-4bc3-4df7-8a09-765794883524