net-mgmt/ipfixcol2: mark this port as suitable only for few architectures, improve port

Port require SSE2 and also 64bit time_t. It work on amd64 and possible
on aarch64 and armv7 (not tested).

Pet portclippy, align lines in Makefile, add substitution for %%USER%%
in start script.

PR: 280850
Approved by: Marek Zarychta <zarychtam@plan-b.pwste.edu.pl> (maintainer)