performance improvement on certain operation

[ldkingvivi]

1. include reduce insert cost to 40% #37 but remove unnecessary changes, add the benchmark on this as well.

before

BenchmarkNetworkEqualIPv4-16          	 5917344	       198 ns/op	      64 B/op	       6 allocs/op
BenchmarkNetworkEqualIPv6-16          	 4486786	       273 ns/op	      42 B/op	       6 allocs/op

after

BenchmarkNetworkEqualIPv4-16          	100000000	        10.6 ns/op	       0 B/op	       0 allocs/op
BenchmarkNetworkEqualIPv6-16          	100000000	        10.9 ns/op	       0 B/op	       0 allocs/op

2. change newPathprefixTrie to not call newPrefixTree, save time on extra parseCIDR and NewNetwork

before

BenchmarkNewPathprefixTriev4-16                                    	 2731194	       440 ns/op	     288 B/op	      12 allocs/op
BenchmarkNewPathprefixTriev6-16                                    	 1610536	       743 ns/op	     456 B/op	      16 allocs/op

after

BenchmarkNewPathprefixTriev4-16                                    	13315774	        88.3 ns/op	      16 B/op	       4 allocs/op
BenchmarkNewPathprefixTriev6-16                                    	 7967464	       153 ns/op	      64 B/op	       4 allocs/op

[coveralls]

Coverage remained the same at 91.281% when pulling 9adafe1 on ldkingvivi:master into 7ff5a0e on yl2chen:master.

[coveralls]

Coverage decreased (-2.2%) to 89.074% when pulling 38ddb96 on ldkingvivi:master into 7ff5a0e on yl2chen:master.