link patches are applied with deprecated rpm macro, builds fail

[pallaswept]

Issue Description

I created a link to an existing package, and edited the resulting _link file to add a patch
The patch was successfully added, the package built successfully, however the linter failed the build:

[   40s] 
[   40s] pam_ssh_agent_auth.spec:56: E: patch-macro-old-format (Badness: 10000)
[   40s] The usage of %patchN is not supported by RPM >= 4.20. The preferred way to
[   40s] apply patches are, in order:  * %autosetup -p1  * %autosetup -N / %autopatch
[   40s] -p1  * %setup / %patch -P <N> -p 1 (upper case P denotes patch number,
[   40s] lower case is the usual patch -p<num> strip level)
[   40s] 

Expected Result

Build completes without linter error

How to Reproduce

1. create a link to an existing package with osc linkpac
2. edit the resulting _link file to add a patch eg <add name="add-argument-default_ssh_auth_sock-and-some-fixes.patch" popt="1"/>
3. commit the changes to build the package
4. See error

[pallaswept]

Not sure if I should be submitting a PR, but hopefully it helps: pretty sure these two lines just need to be slightly altered, to use the new macros

open-build-service/src/backend/BSSrcServer/Link.pm

Line 166 in 6ec8699

print O "%patch$nrx -p$p->{'popt'}\n";

open-build-service/src/backend/BSSrcServer/Link.pm

Line 168 in 6ec8699

print O "%patch$nrx\n";

ie just change
%patch$nrx
to
%patch -P $nrx