Add inlining to pnet_macros_support packets.rs

[infosechoudini]

We should add inlining to all functions that are not part of traits in pnet_macros_support/src/packets.rs

While running benchmarks, it seems to increase the overall speed by 100% for functions that require getting or setting parts of the packet struct.

Without inlining
running 5 tests
test bench_packet_get_source             ... bench:          15 ns/iter (+/- 2)
test bench_packet_immutable_to_immutable ... bench:           2 ns/iter (+/- 0)
test bench_packet_mutable_to_immutable   ... bench:           2 ns/iter (+/- 0)
test bench_packet_new_constructor        ... bench:           1 ns/iter (+/- 0)
test bench_packet_set_source_black_box   ... bench:          17 ns/iter (+/- 0)

With inlining
running 5 tests
test bench_packet_get_source             ... bench:           8 ns/iter (+/- 1)
test bench_packet_immutable_to_immutable ... bench:           2 ns/iter (+/- 0)
test bench_packet_mutable_to_immutable   ... bench:           2 ns/iter (+/- 0)
test bench_packet_new_constructor        ... bench:           1 ns/iter (+/- 0)
test bench_packet_set_source_black_box   ... bench:           9 ns/iter (+/- 3)

by far the speed to parse packets is much slower than nom and nom_derive. This will increase usability of the crate.

[infosechoudini]

additionally add to pnet_macros/src/decorators to be able to handle packet generation better. The above bench with inlining includes that

[infosechoudini]

#555 did this PR for this

[infosechoudini]

Closing! PR Merged!