Two minor optimizations of fdalloc():
Two minor optimizations of fdalloc():

 - if minfd < fd_freefile (as is most often the case, since minfd is
   usually 0), set it to fd_freefile.

 - remove a call to fd_first_free() which duplicates work already done
   by fdused().

This change results in a small but measurable speedup for processes
with large numbers (several thousands) of open files.

PR:		kern/85176
Submitted by:	Divacky Roman <xdivac02@stud.fit.vutbr.cz>
MFC after:	3 weeks

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase