ofctl_utils: Enhance user value conversion
ofctl_utils: Enhance user value conversion

Currently, OFCtlUtil._reserved_num_from_user() fails to convert
an user specified value when it is a numeric string.
This patch enhances this conversion to enable to convert an user
value as follows.

e.g.)
 - Integer: 1 -> 1
 - Numeric string: "1" -> 1
 - Reserved number: "OFPP_ANY" -> 0xffffffff
 - Invalid value: "foobar" -> "foobar" (do not conversion)

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

shinpeimuraoka/ryu,iwaseyusuke/ryu,hisaharu/ryu,gareging/SDN_Framework,fujita/ryu,gareging/SDN_Framework,TakeshiTseng/ryu,TakeshiTseng/ryu,zangree/ryu,TakeshiTseng/ryu,pichuang/ryu,lagopus/ryu-lagopus-ext,fujita/ryu,iwaseyusuke/ryu,fkakuma/ryu,zangree/ryu,shinpeimuraoka/ryu,shinpeimuraoka/ryu,fkakuma/ryu,gareging/SDN_Framework,Tejas-Subramanya/RYU_MEC,fkakuma/ryu,fujita/ryu,lagopus/ryu-lagopus-ext,hisaharu/ryu,iwaseyusuke/ryu,zangree/ryu,Tejas-Subramanya/RYU_MEC,fkakuma/ryu,pichuang/ryu,pichuang/ryu,osrg/ryu,shinpeimuraoka/ryu,Tejas-Subramanya/RYU_MEC,iwaseyusuke/ryu,fujita/ryu,gareging/SDN_Framework,fkakuma/ryu,shinpeimuraoka/ryu,pichuang/ryu,hisaharu/ryu,hisaharu/ryu,osrg/ryu,Tejas-Subramanya/RYU_MEC,zangree/ryu,Tejas-Subramanya/RYU_MEC,osrg/ryu,lagopus/ryu-lagopus-ext,fujita/ryu,TakeshiTseng/ryu,TakeshiTseng/ryu,iwaseyusuke/ryu,gareging/SDN_Framework,osrg/ryu,zangree/ryu,lagopus/ryu-lagopus-ext,hisaharu/ryu,osrg/ryu,lagopus/ryu-lagopus-ext,pichuang/ryu