Fix to http persistence cookie logger irule

when RULE_INIT {

 From http://support.f5.com/kb/en-us/solutions/public/6000/900/sol6917.html
 For example, if the port of the destination server is 8080, the BIG-IP LTM encodes the port as follows:
 8080 = 0x1F90
 Reverse byte order = 0x901F
 0x901F = 36895

set myPortE 36895
set myPortH [format %x $myPortE]
log local0. "\$myPortE: $myPortE, \$myPortH, $myPortH"

 Old, wrong way
log local0. "Old: [expr 0x[substr $myPortH 2 2]][expr 0x[substr $myPortH 0 2]]"

 Updated, correct way
log local0. "New: [expr 0x[substr $myPortH 2 2][substr $myPortH 0 2]]"

 Log output:
 : $myPortE: 36895, $myPortH, 901f
 : Old: 31144
 : New: 8080
}