Bios: support IPv4-mapped IPv6 address length

The existing code will allow ::<ipv4_address> without
any error. However, if the address is expanded like the
below, there will be "length out of range" error:
0000:0000:0000:0000:0000:ffff:xxx.xxx.xxx.xxx

This commit changes the maximum string length of
IPv6 address from 39 to 45, to support IPv4-mapped
IPv6 address.

Change-Id: I8c6e90e5a0ddbf38e7826e5918408b5d29811bfd
Signed-off-by: Asmitha Karunanithi <asmitk01@in.ibm.com>