bind: rename ptrsize to ptr_size in the code

uClibc in commit 70a04a28 #defined ptrsize globally in bits/setjmp.h for
mips. However this is a common variable name and causes build failure
for at least bind.
So rename ptrsize to ptr_size in bind to avoid this. Fixes:
http://autobuild.buildroot.net/results/a92/a92fa5dc5d9d6742d61d4d293f7eac97c5355dfe/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>